CI: tracebacks should be in the main log for cirleCI

[bsipocz]

Currently, the tracebacks are dumped in separate logfiles and a WARNING is raised, so not much to go by for debugging the actual issue without ssh-ing, etc.

Ideally all tracebacks and etc should be included in the main CI log, so one look should be enough to decide something is a fluke failure due to upstream server issues or an actual failures.

Current log looks like this:

reading sources... [100%] index

/home/circleci/project/CS_Catalog_Queries.ipynb: WARNING: Executing notebook failed: CellExecutionError [mystnb.exec]
/home/circleci/project/CS_Catalog_Queries.ipynb: WARNING: Notebook exception traceback saved in: /home/circleci/project/_build/html/reports/CS_Catalog_Queries.err.log [mystnb.exec]
/home/circleci/project/CS_Spectral_Access.ipynb: WARNING: Executing notebook failed: CellExecutionError [mystnb.exec]
/home/circleci/project/CS_Spectral_Access.ipynb: WARNING: Notebook exception traceback saved in: /home/circleci/project/_build/html/reports/CS_Spectral_Access.err.log [mystnb.exec]
looking for now-outdated files... none found
/home/circleci/project/QuickReference.ipynb: WARNING: Executing notebook failed: CellExecutionError [mystnb.exec]
/home/circleci/project/QuickReference.ipynb: WARNING: Notebook exception traceback saved in: /home/circleci/project/_build/html/reports/QuickReference.err.log [mystnb.exec]
/home/circleci/project/UseCase_II.ipynb: WARNING: Executing notebook failed: CellExecutionError [mystnb.exec]
/home/circleci/project/UseCase_II.ipynb: WARNING: Notebook exception traceback saved in: /home/circleci/project/_build/html/reports/UseCase_II.err.log [mystnb.exec]
pickling environment... done
checking consistency... done
preparing documents... done