misc: make hooks behave better on build MRs

commitrefs: handle dist-release commits cleanly

Now maintainer build MRs can get CommitRefs::OK on them too.

jirahook: handle dist-release commits cleanly

Consider a dist-release commit to be a valid Internal commit, rather than
flagging it as an untagged commit, so build MRs can get Jira::OK.

description: add is_dist_release_commit property

These commits are generated by the 'make dist-release' command by
maintainers, and have no jira tag or upstream commit reference in them,
and so they get flagged as problematic by some hooks. Try to identify
them, so we can handle them better.

fixes-hook: do not run on maintainer build MRs

mergehook: don't check against build MRs

It's typically a waste of time to do a comparison against a maintainer's
build MR, as it should simply be incorporating other MRs.

Signed-off-by: Jarod Wilson jarod@redhat.com