Presently we codify the entry point for a job as the "start" callback,
but a more apt name would be "run" to clarify the idea that when this
function returns we consider the job to have "finished," except for
any cleanup which occurs in separate callbacks later.

As part of this clarification, change the signature to include an error
object and a return code. The error ptr is not yet used, and the return
code while captured, will be overwritten by actions in the job_completed
function.
Signed-off-by: NJohn Snow <jsnow@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180830015734.19765-2-jsnow@redhat.com
Reviewed-by: NJeff Cody <jcody@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>