Upstart scripts are being incorrectly identified as SysV init scripts
due to a logic error in the `service` module.
Because upstart uses multiple commands (`/sbin/start`, `/sbin/stop`,
etc.) for managing service state, the codepath for upstart sets
`self.svc_cmd` to an empty string on line 451.
Empty strings are considered a non-truthy value in Python, so
conditionals which are checking the state of `self.svc_cmd` should
explicitly compare it to `None` to avoid overlooking the fact that
the service may be controlled by an upstart script.
We need to handle the string returned by 'default' in the same way we handle
the string returned by 'status' since the resulting flags are compared later.
* Use the newly added 'default' argument to know if the default flags are set
or not.
* Handle that 'status' may either return flags or YES/NO.
* Centralize flag handling logic.
* Set action variable after check if we need to keep going.
Big thanks to @ajacoutot for implementing the rcctl 'default' argument.
* Make the module support enable/disable of special services like pf via rcctl.
Idea and method from @jarmani.
* Make the module handle when the user supplied 'arguments' variable does not
match the current flags in rc.conf.local.
* Update description now that the code tries to use rcctl for everything if it
is available.
Based on input from @jarmani:
* A return value of 2 now means a service does not exist. Instead of
trying to handle the different meanings of rc after running "status",
just look at stderr to know if something failed.
* Skip looking at stdout to make the code cleaner. Any errors should
turn up on stderr.
