packaging: services: ovirt-engine: support absolute path at ENGINE_APPS

this enables to deploy wars of other packages without touching /usr

Related-To: https://bugzilla.redhat.com/show_bug.cgi?id=1059480
Change-Id: I71f5b8850987372d1d785adceebf020d39a474eb
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>