This change introduces to possibility for the consumer application
to change the default oslo.messaging config options.
Same API interface as oslo.db have been taken.
The first option is executor_thread_pool_size.
This option was called rpc_thread_pool_size, but because it's used by
notification and rpc 'executor_thread_pool_size' looks a better name.
Changing executor_thread_pool_size default will be useful for ceilometer
the default of 64 is really to small to consume many notifications at
once for batching them. When is clearly sufficient for rpc stuffs.
Change-Id: Iea0d7a72e38d27c600403c815258aa5eee0d0c8c
d94d6d6892