complain about gerrit ids in commit messages outside Change-Id footer

people use them to refer to related commits. they should use stable
sha1s of merged commits instead.

Change-Id: Ic58aa875aa978dc76948521266741258fd8c94aa
Reviewed-by: Sergio Ahumada <sahumada@blackberry.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>