add "None" cluster when database is empty
add "None" cluster when database is empty

Change-Id: I72e493b3aee4fa0c7cc61f3fcb49502f9b1dad10
Reviewed-on: http://review.couchbase.org/23826
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Pavel Paulau <dd88eded64e90046a680e3a6c0828ceb8fe8a0e7@gmail.com>

pavel-paulau/cbagent,couchbase/cbagent,mikewied/cbagent,ronniedada/litmus,couchbase/cbmonitor,ronniedada/litmus,couchbase/cbmonitor,vmx/cbagent