tools: move common library to its own directory

Makes it easier to build and process in the future

Change-Id: Ibd8752646e5d346863d3b23ac7be3c384d5af90c
Reviewed-on: http://review.couchbase.org/38428
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>