Let scheduler GRPC methods return before calling schedule

[robertnishihara]

The first time a worker calls "ReadyForNewTask", all of the remote functions will be added to a queue to be exported to the worker. Then schedule is called, which tries to export all of the remote functions to the worker. If the size of the worker's message queue is smaller than the number of exported remote functions, then this will freeze, and ReadyForNewTask will never return. The solution is to allow schedule to be called only after ReadyForNewTask has returned.

This problem can be easily exposed by changing the default size of the message queue in ipc.h to a small number like 5 and then running the tests.