Currently, when creating a cherry-pick and specifying a base,
if the base is an open change, we should show the created
cherry-pick and the base as related changes. However, this doesn't
happen.
This change ensures that those changes will have the same "groups"
thus the GetRelated endpoint will identify those changes as related.
Also removed legacy workaround for RevertSubmission that allowed
those changes to be related.
Change-Id: Id712918b2fc8e25ea997a668c1137fd59fd687b6
d39e31c156