gerrit: Add support for on changed restored/abandoned.

These triggers are supported starting at gerrit-trigger 2.8.0.

Using thoses triggers in a previous version should not cause any
problem.

Change-Id: I388cfb9424dd16dc436010c492e59dd0e896b69a
Reviewed-on: https://review.openstack.org/24264
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Anita Kuno <akuno@lavabit.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins
gerrit: Add support for skipVote.

Newer versions of gerrit-trigger permit builds to forbear, depending of
the build outcome (success, failure, etc.).

This capability is exposed in jenkins-job-builder, with suitable
defaults.

Change-Id: I25e267459b93b8e18a690c4d38989196ca1298f3
Reviewed-on: https://review.openstack.org/24265
Reviewed-by: James E. Blair <corvus@inaugust.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Anita Kuno <akuno@lavabit.com>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins