PCBC-178: Add support for connection_timeout

Change-Id: I350f1137f9673b9682cf92e7830a005168ac701b
Reviewed-on: http://review.couchbase.org/25439
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>