virsh domjobinfo: Do not return 1 if job is NONE

https://bugzilla.redhat.com/show_bug.cgi?id=1006864

Commit 38ab1225 changed the default value of ret from true to false but
forgot to set ret = true when job is NONE. Thus, virsh domjobinfo
returned 1 when there was no job running for a domain but it used to
(and should) return 0 in this case.
(cherry picked from commit f084caae)

tools/virsh-domain.c

@@ -4931,6 +4931,7 @@ cmdDomjobinfo(vshControl *ctl, const vshCmd *cmd)
     case VIR_DOMAIN_JOB_NONE:
     default:
         vshPrint(ctl, "%-12s\n", _("None"));
+        ret = true;
         goto cleanup;
     }