Fix the email flood caused by not handling the yield logic properly

The notification logic handled the internal loop only
(in _perform_engine_actions), but forgot to handle the loop around
that method. That caused an email flood with the same information.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1032644
Change-Id: I4f35d85472f9e27bad222254a4d5c81b845d6282
Signed-off-by: Martin Sivak <msivak@redhat.com>