make _view_cleanup endpoint cluster aware
make _view_cleanup endpoint cluster aware

Currently _view_cleanup endpoint is not cluster aware, only deletes
indexes on the node that gets the request. This will make it cluster
aware, deleting unused indexes on all nodes.

JIRA: COUCHDB-2779

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb