Add attempts logic for jobs

Today, if a job is aborted, zuul will launch said job until success /
failure.  If the job continues to abort, it will loop forever.  As a
result, we now added the ability to limit this.  By default we'll try
to relaunch an aborted job a total of 3 times, before RETRY_LIMIT is
returned as the result.

Change-Id: Ie26fdc29c07430ebfb3df8be8ac1786d63d7e0fe
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
8 files changed