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/socket.io.js

@@ -102,7 +102,7 @@ describe('socket.io', function () {
 	});
 
 	after(function (done) {
-		done();
+		db.emptydb(done);
 	});
 
 });