indexer: Use cluster address to discover about kv nodes

Currently indexer uses local projector address to discover about
kv nodes. This makes it impossible to run index server only node
in a cluster setup. This changes makes it possible for ns_server
to provide local cluster address to the indexer and indexer can
discover kv addresses by contacting cluster endpoint.

Change-Id: Ief9071f831ad3b5f59ec3fe2aabd9c7b5420796a
Reviewed-on: http://review.couchbase.org/43681
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>