tools: Fixes proper ovirt-engine-notifier shutdown

Removes System.exit(0) call from shutdown hook to shutdown service
properly.
Removes schedulers shutdown call from exception handling since their
shutdown is executed in shutdown hook.

Change-Id: I3af05da64ef213520ee013e35c21c3633bcc37e0
Bug-Url: https://bugzilla.redhat.com/1007443
Signed-off-by: Martin Perina <mperina@redhat.com>