Allow master logging in --metrics mode

cluster.worker is null in the master, not empty.

Introduced in 1c92540324e34774209d926e977f40c1488a6790.
runctl: clarify fork response and usage
Merge pull request #48 from strongloop/feature/clarify-fork

runctl: clarify fork response and usage
control: refactor control channel naming
run: fix --no-channel option

It was actually opening a channel called "false".
run: support control and exit via node ipc

All commands available to `slc runctl` over local domain sockets are
made available to a parent node process, if it establishes an ipc
connection to the supervisor (see `child_process.fork()`).

Also, when the ipc connection is disconnected (either explicitly, or
because the parent process exited, the child can't tell the difference),
the supervisor will exit to prevent process leaks.
Merge pull request #49 from strongloop/feature/pmctl

Feature/pmctl
runctl: add heap-snapshot command