Migrate each instances of a host to another.

Added a new extension that adds the ability for admins to migrate all
servers of a host to another available hosts.

Implements blueprint host-servers-migrate
Change-Id: I4e9c4be7ceb098d7a3bf553fd44addd46e8bce72
Merge "Migrate each instances of a host to another."
Adds support for ExtendedFloatingIps APi extension

Allow a floating IP to be associated to a specific fixed IP

This is the client side of:
https://review.openstack.org/#/c/26113/15

Change-Id: I05f8a0dc60268535231b95a6664719015f67a318
Merge "Adds support for ExtendedFloatingIps APi extension"