Convert job queue's RPC to generated code

With these changes job queue RPC will finally show up on the lock
monitor. See below for an example. A job queue-specific class is used to
restrict the use of a static list for name resolution to the job queue.
Further improvements can be made to not re-create the whole RPC client
for every call (e.g. by using a more dynamic resolver), but for now this
works.

rpc/node8.example.com/jobqueue_update Jq8/Job9/TEST_DELAY

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>