require eventlet in RPC service.

Ubuntu 14.04 forces librabbitmq when kombu is used
Unfortunately it forces a version that has a crash
bug.  Calling eventlet.monkey_patch() tells kombu
to use libamqp instead.

Change-Id: I9bc2073f620391e5d0b384142a4d4b0ad7104fcf
Closes-Bug: 1365679
Merge "require eventlet in RPC service."