If the start webhob command fails we need to kill any process that's using bitbake.lock and to delete whbmain.pid file. Otherwise we'll be warned that the system is already running even if it isn't working properly, and cannot be stopped or restarted correctly with these files present or involved in another process.
Fixes to webhob start script commited in webhob-poky/master
Verified in master:e4c23f7bcb79072ea6028fbdf8f3f0dc17a63371.