search tests

new method emptydb
use emptydb instead of flushdb, flushdb  removes indices for mongo which
breaks search tests
initialize meta.config properly in tests
enable nodebb-plugin-dbsearch for tests

src/database/mongo/main.js

@@ -12,6 +12,13 @@ module.exports = function (db, module) {
 		});
 	};
 
+	module.emptydb = function (callback) {
+		callback = callback || helpers.noop;
+		db.collection('objects').remove({}, function (err) {
+			callback(err);
+		});
+	};
+
 	module.exists = function (key, callback) {
 		if (!key) {
 			return callback();