fix Singleton.__call__ error

fix Singleton.__call__ error
Fixing Node.monitor() to read entire prompt marker.

Applying @cdburkard fix to #322
updaing build.py to use 12.04.5 and extract kernel using noload
Merge branch 'master' of github.com:mininet/mininet
kill all child processes to avoid race condition and no controller shutdown
added controller.stop() back in
Merge pull request #356 from cdburkard/patches/stop_controller

fix for controller shutdown - send SIGHUP rather than SIGKILL