engine: Simplify iteration over interfaces

Instead of iterating over all of the interfaces
fetched from the DB, and attempting to match
their equivalent as report by vdsm by name
(also via iterating over all of the host nics),
a map simplify the matching action.

Change-Id: I093a5c6d0f77bcd038a3c7894af343d87687608a
Signed-off-by: Moti Asayag <masayag@redhat.com>