Sync rpc changes from oslo-incubator

Syncs:

  93ee6e3 Add generic serialization support
  df7ea83 Allow RPC_API_NAMESPACE on RpcProxy objects
  1d7920a Extract matchmaker_ring to own module
  aa89d8b Support capping message versions in the client.

Change-Id: I80a2671997e8074bef9d1ef230ca3956888265e6
Merge "Sync rpc changes from oslo-incubator"