Grab oonib's pid from the .pid file for the CI test process killer.

 * travis-lint checks out okay:
(oonib)∃!isisⒶwintermute:~/code/torproject/ooni-backend ∴ date
Sun Apr 21 07:55:19 UTC 2013
(oonib)∃!isisⒶwintermute:~/code/torproject/ooni-backend ∴ travis-lint
Hooray, /home/isis/code/torproject/ooni-backend/.travis.yml seems to be solid!
Only import txtorcon classes which are in use.
Fix the "directory not empty" error when removing the tmp tor_datadir.