restapi: Display type is not inherited correctly from templates

In API, default display type is applied to a new VM when created from a
template with a different display type.

Fixed by correcting corresponding mapper class.

Change-Id: I61b410f258afb529d7309d0f68f223d4984c0514
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=986668