Couchbase sync gateway

Resolves jira task BROOKLYN-9
Could use `Predicates.and(Predicates.instanceOf(CouchbaseNode.class), EntityPredicates.attributeEqualTo(CouchbaseNode.IS_IN_CLUSTER, true)`, rather than declaring a new predicate.

For general background reading, see https://code.google.com/p/guava-libraries/wiki/FunctionalExplained#Caveats and also the discussion at https://groups.google.com/forum/#!msg/jclouds-dev/f-3QY6EKum4/UVyjHTjT8WIJ (in particular Adrian Cole's "summarize my view" e-mail and Tim Peierls' reply).