ReviewCommand: Don't add message twice on abandon or restore

When abandoning or restoring a change via the --abandon or --restore
option, and giving a message with the --message option, the message was
being added twice. Once by the 'review' and once by the abandon or
restore.

This was already fixed once in change I9c7e81599 which was included in
Gerrit version 2.6, but was then re-introduced by I2240759ba which was
included in version 2.9.

Fix it, and add an acceptance test to make sure it doesn't get broken
again.

Change-Id: I92f8fd98d75c2b1dd96c91f404be3943109c3519
2 files changed