[masakari] Add a rpc api for ping check

Similar to Nova, I think it would be good to add ping api to masakari engine for rpc health check. This can be used for reading business and lifestyle check in Masakari distributed to Kubernetes through OpenStack Helm. Currently, there is no health check for masakari-engine in openstack-helm project, but it would be good to add it. Blueprint: https://blueprints.launchpad.net/masakari/+spec/add-a-rpc-api-for-ping