Ghost status doc and fix stop/kill/restart

a little doc for #2419 , and some code that tests to see if the pid is still running #3231 (just ``os.FindProcess`` is not enough (all the time))

Should the Pid test also be added to startup? I didnt move it into State as that looks atm to be a simplistic data object, but the code is basically an ``container.State.isReallyRunning()``