NCBC-310: Amendment #4 - added connection pool 'growth'

This commit enables the connection pool to grow based upon resource demand
from the MinPoolSize to the MaxPoolSize.

Change-Id: I188b9852282812b85a58e5548c9c70f2645fb22c
Reviewed-on: http://review.couchbase.org/30437
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>