[FAB-12176] Private data and metadata writes

This fix lets the gossip private data coordinator recognize not only
regular writes to private data keys, but also updates of the metadata.

Change-Id: I41ac4dcdc929e1d2390a1eb75684d01c37264f4c
Signed-off-by: Matthias Neugschwandtner <eug@zurich.ibm.com>

gossip/privdata/coordinator.go

@@ -855,7 +855,7 @@ func containsWrites(txID string, namespace string, colHashedRWSet *rwsetutil.Col
 		logger.Warningf("HashedRWSet of tx %s, namespace %s, collection %s is nil", txID, namespace, colHashedRWSet.CollectionName)
 		return false
 	}
-	if len(colHashedRWSet.HashedRwSet.HashedWrites) == 0 {
+	if len(colHashedRWSet.HashedRwSet.HashedWrites) == 0 && len(colHashedRWSet.HashedRwSet.MetadataWrites) == 0 {
 		logger.Debugf("HashedRWSet of tx %s, namespace %s, collection %s doesn't contain writes", txID, namespace, colHashedRWSet.CollectionName)
 		return false
 	}