LU-3568 contrib: ignore initial comments

Sometimes, git likes to insert "git status" commentary
at the top of an auto-generated commit message starter
file. If the committer carelessly neglects to remove
the stuff, the script thinks the message has a missing
commit summary line.

* contrib/tests/test-commit-msg.sh: pass through xtrace setting
* contrib/tests/commit.ok_commit: This message with cruft
* contrib/commit-msg: use a flag instead of a line number to see
  if we still need to process the summary line.

Signed-off-by: Bruce Korb <bruce_korb@xyratex.com>
Reviewed-by: Cheng Shao <cheng_shao@xyratex.com>
Xyratex-bug-id: MRP-1160
Change-Id: I46e2951f2e28cbbf53bf2e96e420ddcea7c0d991
Reviewed-on: http://review.whamcloud.com/6921
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>