Mock should use a empty list instead of null for the servers.

Change-Id: I103606e82f609231846998b59719fa170bd4624a
Reviewed-on: http://review.couchbase.org/29466
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>