bug: doesnt check if pid is already running

ran into a weird bug today where one of my .pid files in monu was 415, but I had another process running as pid 415 and monu couldn't kill it (it would give me a EPERM error and crash the app if I tried to kill/restart).

Killing process 415 (it was some other app I was running) fixed the issue. So to fix this I guess we should check on startup if the pid exists already?
