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

test/database/sorted.js

@@ -696,6 +696,6 @@ describe('Sorted Set methods', function () {
 
 
 	after(function (done) {
-		db.flushdb(done);
+		db.emptydb(done);
 	});
 });