size-check: add capability to report bugs for oversize images
By popular demand...let's do this! Adds a dependency on
python-bugzilla. Now, with the `-b` argument, the `size-check`
subcommand will file bugs on over-size images. There will be
one bug per image per release; if the bug already exists a new
comment will be added and the bug will be re-opened if closed.
If the image is a release-blocking one, then on creation the
bug will be set to block both Beta and Final blocker trackers
for the release.
Signed-off-by: Adam Williamson <awilliam@redhat.com>