core: [ExternalTasks] Step cannot be ended as...

[ExternalTasks] Step cannot be ended as not successful

Changing the ExecutionHandler:;endStep code to update the step status
and its job status as well in a case of failure.

Change-Id: I7da6e75cf48c9639ee4562885cfc2ab38da7f278
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=988088
Signed-off-by: Eli Mesika <emesika@redhat.com>