RestApiException (and any subclass of it) is caught and rethrown as
a RestApiException with a generic message. This causes the actual
exception type and message to be lost.
Don't catch RestApiException; allow the original to propagate.
Also add tests in ChangeIT to verify behavior when rebasing with and
without the rebase permission.
Change-Id: Ia303dcf0b7158aafa82adfaeeaabd76a8a980b15
52e6bc98b1