Fixed various memory leaks

dbuser.c: key.user value was never freed
skygw_utils.cc: replace_literal values were not always freed

server/core/dbusers.c

@@ -388,7 +388,7 @@ getUsers(SERVICE *service, struct users *users)
 	memcpy(users->cksum, hash, SHA_DIGEST_LENGTH);
 
 	free(users_data);
-
+	free(key.user);
 	mysql_free_result(result);
 	mysql_close(con);
 	mysql_thread_end();