Add qos_policy_id to floating IP, then the user could set/update
the binding QoS policy of a floating IP.
APIImpact: a new parameter qos_policy_id was added to floating IP
related API.
Partial-Bug: #1596611
Partially-Implements blueprint: floating-ip-rate-limit
Change-Id: I4efe9e49d268dffeb3df4de4ea1780152218633b