Spell out unsupported command or change to initctl error string

[troglobit]

While going through the logs of one of our systems I found this. An log messages of an unsupported command during bootstrap. This log message is not really helpful to the user, we call initctl at many places in our system, so it would be better to either extend the log message with more information or return it from initctl instead.

Mar 10 06:49:19 infix finit[1]: api_cb():Unsupported command in runlevel S and 6/0.