telemetry: allow to install collector separately from mongodb

Stop to require MongoDB validation (this provider requies MongoDB
working on the same node) so we can install MongoDB nodes outside
Telemetry Collector service.

This patch is a workaround until:
https://github.com/puppetlabs/puppetlabs-mongodb/pull/200

is merged so we can use the code in this module.
See https://review.openstack.org/179824

Change-Id: I80b102c3801efea262e6572fce1f64eb8a9a67ad

manifests/telemetry/collector.pp

@@ -46,7 +46,6 @@ class cloud::telemetry::collector(
   class { 'ceilometer::db':
     database_connection => $db_conn,
     sync_db             => true,
-    require             => Mongodb_conn_validator['mongodb'],
   }
   class { 'ceilometer::collector': }