Include hosted engine plugin into iso form 3.5 on

From 3.5 on we want to include the hosted-engine plugin by default into
the iso for oVirt.

Change-Id: Idda19745018541a51866aca2108510e67c907c03
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1038616
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>