Floating IP show must reference router ID if exist

When a floating IP is associated to a port which its network is link to
a router, that floating IP should reference the router ID.
The schema change and logical router does not have anymore VMI ref for
interface. Only for the gateway.

Change-Id: Ic7d084fd745bbca37165b77f276019152a70740d
Closes-Bug: #1401827
(cherry picked from commit 4dfbb65e2ca8f544812aee7e3e331dc1baa72cde)
Merge "Floating IP show must reference router ID if exist" into R2.0