PCBC-192: Use persistent connections by default

Change-Id: If0072da4095672afadc70f6e5ace577e13e58125
Reviewed-on: http://review.couchbase.org/24388
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>