runctl: don't attach runctl server in workers

Workers have their node IPC channel attached to the supervisor/cluster
master, and only the targetctl messages are supported on it. Attaching
both runctl and targetctl to the node IPC channel causes every message
to received by both... which goes poorly.
Merge pull request #51 from strongloop/feature/workers-dont-do-runctl

runctl: don't attach runctl server in workers