restapi: [RFE] Display Address Override

Detailed description:
http://wiki.ovirt.org/wiki/Features/Display_Address_Override

Added display_address optional string field to Host.

Change-Id: I105881365d2c23638a1a9ad4db3b82a352f039e3
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>