jobs: remove ret argument to job_completed; privatize it

Jobs are now expected to return their retcode on the stack, from the
.run callback, so we can remove that argument.

job_cancel does not need to set -ECANCELED because job_completed will
update the return code itself if the job was canceled.

While we're here, make job_completed static to job.c and remove it from
job.h; move the documentation of return code to the .run() callback and
to the job->ret property, accordingly.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20180830015734.19765-9-jsnow@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
diff --git a/trace-events b/trace-events
index c445f54..4fd2cb4 100644
--- a/trace-events
+++ b/trace-events
@@ -107,7 +107,7 @@
 # job.c
 job_state_transition(void *job,  int ret, const char *legal, const char *s0, const char *s1) "job %p (ret: %d) attempting %s transition (%s-->%s)"
 job_apply_verb(void *job, const char *state, const char *verb, const char *legal) "job %p in state %s; applying verb %s (%s)"
-job_completed(void *job, int ret, int jret) "job %p ret %d corrected ret %d"
+job_completed(void *job, int ret) "job %p ret %d"
 
 # job-qmp.c
 qmp_job_cancel(void *job) "job %p"