Allow scheduler manager NoValidHost exception to pass over RPC

Calls to scheduler.manager.select_hosts are expected to throw NoValidHost
exceptions if no hosts match such requests. For the exception to be passed
over RPC, the method must be decorated with:

@rpc_common.client_exceptions(exception.NoValidHost)

Resolves bug 1192693.

Change-Id: If9d1f15ff1239e422067893f9d837c41e5f5474d
Merge "Allow scheduler manager NoValidHost exception to pass over RPC"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp