Fix FloatingIP Namespace creation in DVR for Late Binding

Fix FloatingIP Namespace creation in DVR for Late Binding

DVR has dependency on the portbinding host to determine
where to start the FloatingIP Namespace when floatingip
is configured. But when we assign a floatingip to a port
that is not bound, even though the API will succeed, the
FloatingIP Namespace will not be created by the Agent and
so the FloatingIP will not be functional.

This patch addresses the issue by creating the Namespace
and configuring the rules when the late binding happens.

The agent will be requesting the FIP agent gateway port,
if required and then proceed to configure the FloatingIP
Namespace.

Change-Id: I9b9158bddb626c2bb535acd709452560546fd184
Closes-Bug: #1447034
Closes-Bug: #1460408