Zuul internally merges or cherry-picks changes before running jobs
and gerrit-git-prep now uses the output of that. Therefore, merge
jobs are redundant. However, some projects have no gate tests,
so create a noop job for those projects so Zuul has something to run.
As long as it doesn't actually do anything with a git repo, it can
be shared by all projects.
* Remove definitions of merge jobs in jjb.
* Add a new singleton 'gate-noop' job.
* Remove invocations of -merge jobs in zuul, replacing them
with -noop jobs if they are the only jobs for a pipeline.
* Update new job documentation to mention gate-noop, and lack
of need to update projects.yaml if not using python-jobs.
Change-Id: I56d3f0f99b2f05780fc82222854db4f1c8f68b57
Reviewed-on: https://review.openstack.org/18246
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Approved: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Tested-by: Jenkins
e04970cc53