* stable-2.12:
Update cookbook submodule
MergeValidationListener: Expose the caller in onPreMerge() method
Correctly detect symlinked log directory on startup
RebaseIfNecessary: Use submitter identity as the committer
Fix schema migration (115) when updating from Gerrit < 2.11
Hide avatar image when there are no avatars available
Add back ListChangesOption.DRAFT_COMMENTS
Change-Id: Ibaf1264332fdc30db0f0f548121db728f78927ae
394e6345ab