Connection Manager/Socket Pool

This introduces a connection manager with pooling options to allow for
better utilization and caching of sockets

Change-Id: Ia2b306f000d01a9443589b0cba2a45b5205a9319
Reviewed-on: http://review.couchbase.org/32789
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>