`update` can now takes several job names

Just like `delete` can accept several jobs names as argument, this patch
let us do the same with `update`.

* builder.update_jobs now filter the jobs against a list
* renamed 'update' argument 'name' to 'names' to make it clear it
  accepts several job names.

Change-Id: I4bcebd98073ec89e172afbec59b93d14de6620ff
Reviewed-on: https://review.openstack.org/24160
Reviewed-by: Anita Kuno <akuno@lavabit.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins