Missing dependency on packaging

[krzk]

'packaging' module (e.g. python3-packaging on Ubuntu) is required for grok-fsck:

$ grok-fsck -v --repack-only -c /etc/grokmirror/kernel.conf
Analyzing /var/lib/mirror/manifest.js.gz
Traceback (most recent call last):
  File "/usr/local/bin/grok-fsck", line 11, in <module>
    sys.exit(command())
  File "/usr/local/lib/python3.6/dist-packages/grokmirror/fsck.py", line 1392, in command
    opts.repack_all_quick, opts.repack_all_full)
  File "/usr/local/lib/python3.6/dist-packages/grokmirror/fsck.py", line 1367, in grok_fsck
    fsck_mirror(config, force, repack_only, conn_only, repack_all_quick, repack_all_full)
  File "/usr/local/lib/python3.6/dist-packages/grokmirror/fsck.py", line 657, in fsck_mirror
    if commitgraph and not grokmirror.git_newer_than('2.18.0'):
  File "/usr/local/lib/python3.6/dist-packages/grokmirror/__init__.py", line 101, in git_newer_than
    from packaging import version
ModuleNotFoundError: No module named 'packaging'

This dependency should be added to setup.py.