Port floating_ip_pools extention to v2.1

This patch ports floating_ip_pools extention from v2 to v2.1,
and have v2 unit test cases shared between v2.1 and v2.
Partially implements blueprint v2-on-v3-api

Change-Id: I0b34358db08a29e76a59b22a0992abc88296058d
Merge "Port floating_ip_pools extention to v2.1"