Do not start fuse again if already running

Clean up the pid file if Fuse is stopped, so it does not cause failures due to references to the invalid pid it contains.

In general I think this logic needs some more scrutiny, but this will fix the 3 bugs currently open.
https://bugzilla.redhat.com/show_bug.cgi?id=1086739
https://bugzilla.redhat.com/show_bug.cgi?id=1085781
https://bugzilla.redhat.com/show_bug.cgi?id=1085766