Improve error logging

[kshtsk]

We can see error messages like that?

2020-07-13T13:07:14.353 INFO:teuthology.orchestra.run.target-ses-060.stdout:Failure in minion: target-ses-060.ecp.suse.de
2020-07-13T13:07:14.359 INFO:teuthology.orchestra.run.target-ses-060.stdout:__id__: download ceph container image
2020-07-13T13:07:14.360 INFO:teuthology.orchestra.run.target-ses-060.stdout:__run_num__: 60
2020-07-13T13:07:14.361 INFO:teuthology.orchestra.run.target-ses-060.stdout:__sls__: ceph-salt.cephtools
2020-07-13T13:07:14.362 INFO:teuthology.orchestra.run.target-ses-060.stdout:changes:
2020-07-13T13:07:14.363 INFO:teuthology.orchestra.run.target-ses-060.stdout:  pid: 12811
2020-07-13T13:07:14.364 INFO:teuthology.orchestra.run.target-ses-060.stdout:  retcode: 1
2020-07-13T13:07:14.365 INFO:teuthology.orchestra.run.target-ses-060.stdout:  stderr: "INFO:cephadm:Pulling latest registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph...\n\
2020-07-13T13:07:14.366 INFO:teuthology.orchestra.run.target-ses-060.stdout:    INFO:cephadm:Non-zero exit code 125 from /usr/bin/podman pull registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph\n\
2020-07-13T13:07:14.367 INFO:teuthology.orchestra.run.target-ses-060.stdout:    INFO:cephadm:/usr/bin/podman:stderr Trying to pull registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph...\n\
2020-07-13T13:07:14.368 INFO:teuthology.orchestra.run.target-ses-060.stdout:    INFO:cephadm:/usr/bin/podman:stderr   Get https://registry.suse.de/v2/: x509:\
2020-07-13T13:07:14.370 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ certificate signed by unknown authority\nINFO:cephadm:/usr/bin/podman:stderr\
2020-07-13T13:07:14.371 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ Error: error pulling image \"registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph\"\
2020-07-13T13:07:14.373 INFO:teuthology.orchestra.run.target-ses-060.stdout:    : unable to pull registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph:\
2020-07-13T13:07:14.374 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ unable to pull image: Error initializing source docker://registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph:latest:\
2020-07-13T13:07:14.375 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ error pinging docker registry registry.suse.de: Get https://registry.suse.de/v2/:\
2020-07-13T13:07:14.375 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ x509: certificate signed by unknown authority\nTraceback (most recent call last):\n\
2020-07-13T13:07:14.377 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \  File \"/usr/sbin/cephadm\", line 4761, in <module>\n    r = args.func()\n \
2020-07-13T13:07:14.378 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ File \"/usr/sbin/cephadm\", line 1145, in _infer_image\n    return func()\n\
2020-07-13T13:07:14.379 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \  File \"/usr/sbin/cephadm\", line 2234, in command_pull\n    call_throws([container_path,\
2020-07-13T13:07:14.380 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ 'pull', args.image])\n  File \"/usr/sbin/cephadm\", line 846, in call_throws\n\
2020-07-13T13:07:14.382 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \    raise RuntimeError('Failed command: %s' % ' '.join(command))\nRuntimeError:\
2020-07-13T13:07:14.383 INFO:teuthology.orchestra.run.target-ses-060.stdout:    \ Failed command: /usr/bin/podman pull registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph"
2020-07-13T13:07:14.384 INFO:teuthology.orchestra.run.target-ses-060.stdout:  stdout: ''
2020-07-13T13:07:14.385 INFO:teuthology.orchestra.run.target-ses-060.stdout:comment: 'Command "cephadm --image registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph
2020-07-13T13:07:14.386 INFO:teuthology.orchestra.run.target-ses-060.stdout:  pull
2020-07-13T13:07:14.387 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.388 INFO:teuthology.orchestra.run.target-ses-060.stdout:  " run'
2020-07-13T13:07:14.389 INFO:teuthology.orchestra.run.target-ses-060.stdout:duration: 1477.83
2020-07-13T13:07:14.390 INFO:teuthology.orchestra.run.target-ses-060.stdout:name: 'cephadm --image registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph
2020-07-13T13:07:14.391 INFO:teuthology.orchestra.run.target-ses-060.stdout:  pull
2020-07-13T13:07:14.392 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.393 INFO:teuthology.orchestra.run.target-ses-060.stdout:  '
2020-07-13T13:07:14.394 INFO:teuthology.orchestra.run.target-ses-060.stdout:result: false
2020-07-13T13:07:14.395 INFO:teuthology.orchestra.run.target-ses-060.stdout:start_time: '13:07:12.824698'
2020-07-13T13:07:14.396 INFO:teuthology.orchestra.run.target-ses-060.stdout:state: 'cmd_|-download ceph container image_|-cephadm --image registry.suse.de/suse/sle-15-sp2/update/products/ses7/milestones/containers/ses/7/ceph/ceph
2020-07-13T13:07:14.397 INFO:teuthology.orchestra.run.target-ses-060.stdout:  pull
2020-07-13T13:07:14.398 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.399 INFO:teuthology.orchestra.run.target-ses-060.stdout:  _|-run'
2020-07-13T13:07:14.400 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.401 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.429 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.430 INFO:teuthology.orchestra.run.target-ses-060.stdout:Finished execution of ceph-salt formula
2020-07-13T13:07:14.430 INFO:teuthology.orchestra.run.target-ses-060.stdout:
2020-07-13T13:07:14.431 INFO:teuthology.orchestra.run.target-ses-060.stdout:Summary: Total=1 Succeeded=0 Failed=1
2020-07-13T13:07:14.944 DEBUG:teuthology.orchestra.run:got remote process result: 2

Can the logger be improved so "stderr" and "stdout" represent human readable multi-line text instead of escaped text, yaml supports | for its records.