Port to oslo.messaging

Now that all preparations are done, actually port the code to use
oslo.messaging. This patch does as little as possible. Follow up patches
that refactor and cleanup the code and configuration files, will be
merged later. The reason for this is to make the patch as slim as
possible, to make review process more smooth and concentrated.

Details:
* neutron/common/rpc.py:
  - added init() and cleanup() to set global RPC layer state.
  - added utility functions: get_server(), get_client(), get_notifier()
    that wrap up oslo.messaging API a bit, enforcing eventlet executor
    and setting serializer, among other things.
  - removed PluginRpcDispatcher, instead introduced PluginRpcSerializer
    to use as a default serializer for API callbacks.

* neutron/common/rpc_compat.py:
  - emulated incubator RPC layer behaviour thru previously introduced
    stub classes (RpcCallback, RpcProxy, ...) using new oslo.messaging
    API.
  - switched to using new oslo.messaging exception types.

* neutron/service.py:
  - expect multiple RPC listeners that are of MessageHandlingServer
    type, not GreenThread.

* neutron/common/config.py:
  - initialize RPC layer in init()

* setup.cfg:
  - added entry points for old notifier drivers to retain backward
    compatibility.

* neutron/tests/...:
  - introduced fake_notifier to replace impl_fake.
  - faked out consume_in_thread() to avoid starting RPC listeners when
    running unit tests.
  - used 'fake' transport driver.
  - made sure neutron.test.* exceptions are caught.
  - initialize and clean up RPC layer for each test case.

* Ported all affected code from using neutron.openstack.common.notifier
  API to oslo.messaging.Notifier.

* rpc.set_defaults() was renamed to rpc.set_transport_defaults()

* other changes not worth mentioning here.

blueprint oslo-messaging

DocImpact

Change-Id: I5a91c34df6e300f2dc46217b1b16352fcc3039fc
Renamed start_rpc_listener -> start_rpc_listeners

Now that we explicitly start multiple RPC servers, renamed the method to
reflect behaviour.

blueprint oslo-messaging

Change-Id: I7c51cc1b44b4b4c8899255b9bedce1792c38634e
Renamed consume_in_thread -> consume_in_threads

Now that we explicitly start multiple RPC servers, and each listener is
served in a separate thread, renamed the method to reflect new
behaviour.

blueprint oslo-messaging

Change-Id: I616f3a23e23e982e13f9b56ce417ca3623247f95
Renamed argument for create_consumer[s]

Now that we don't have explicit dispatcher class to pass into RPC layer,
and we pass a list of endpoints instead, fix names for corresponding
arguments of the functions.

blueprint oslo-messaging

Change-Id: I84c6428574c155cdfaf535210b236c58604de268
Merge "Port to oslo.messaging"
Merge "Renamed start_rpc_listener -> start_rpc_listeners"
Merge "Renamed consume_in_thread -> consume_in_threads"
Merge "Renamed argument for create_consumer[s]"