Added readiness check to avoid errors during topology changes

[edescourtis]

erpc and nodes show up faster than the applications can start in some cases leading to requests being routed to booting nodes. A workaround is possible in the RPC call, but it leads to the proliferation of error handling code, so it would be better to wait for the nodes to be ready.

[eric0fw]

@bitwalker Let me know if you want me to change something.