core: SpmStopOnIrs - set result

When executing SpmStopOnIrs we should set the return value to be
as the return value of the command that's being executed, otherwise the
caller can't tell what actually happend.

Change-Id: I5eb2a4c788ef5cf571a8de150355c85e3a9ae77a
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1130222
Signed-off-by: Liron Aravot <laravot@redhat.com>