pmctl watchdog tests

For https://github.com/strongloop-internal/scrum-nodeops/issues/219

Add some tests.
Intentional, and identical to sl-runctl usage: https://github.com/strongloop/strong-supervisor/blob/master/bin/sl-runctl.txt#L21

Jamming all the explanatory notest int othe rightmost 30 columns is pretty ugly, and and unreasonably bloats the usage message.

Mostly we strive to not need this kind of explanatory text, or else we put it after all the options. But putting it after has problems, particularly when there are this many options: you get the explanation divided across a half-line summary, and then the details far below mixed in with other information.