Fix unhandled InvalidServerState exceptions in server start/stop

Catch InvalidServerState exceptions in the server start/stop api
and return a 409 conflict rather than causing 500 errors

Closes-Bug: 1266379

Change-Id: I9d2437319d2cef93b9b10184e257acbd8eb45359
Merge "Fix unhandled InvalidServerState exceptions in server start/stop"