PYCBC-221: Rename 'conncache' to 'config_cache'

Old parameter name is still supported

Change-Id: Ib98fa2c7b303d56b55ef8aeee03b79b130892197
Reviewed-on: http://review.couchbase.org/32385
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>