Prevent new patchset notification emails for trivial rebase

It is usually not interesting to know that the change was rebased.

Sending mail for this kind of changes distracts the users from
valuable notifications, and is considered spam by many users[1].

Some users completely ignore all mails from gerrit because of this.

[1] https://groups.google.com/d/msg/repo-discuss/fFX_MZerngM/BCitSBFDvSAJ

Change-Id: I7b61ae8445d6fd5dcce2b9a4710609eef43546a5
4 files changed