Proxy floating IP calls to quantum

Fixes bug 1023169. Also fixes bug 1031119.

In Folsom, floating IP support is moved to Quantum. By this commit floating IP
calls to nova are proxied to Quantum and nova command can be used to manage
floating IPs.

pip-requires is also updated and now requires python-quantumclient >=2.1 which
supports floating IP feature in Quantum.

Change-Id: I2c32948a8fe291601216dc62d546da64a8fb8428
(cherry picked from commit 7948b7a572e33e3fd541e27f2617d832eb43b504)