classes/buildhistory: include metadata revisions in commit message
We do already commit these into the repository itself, but have them in
the commit message as well as a reference. As part of this, refactor out
running "git commit" into a separate function so we don't have to
duplicate the code in the two places we call it.
Implements [YOCTO #7966].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
