default val for __new__() in RestConnection

removes warning where importing rest_client
complains that __new__ takes 2 args.
doesn't occur at runtime, but somehow
import module tries to call this method with
no args

Change-Id: I06a264507714201062e2b8459053b3752789056c
Reviewed-on: http://review.couchbase.org/25383
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>