Add functional tests for /disco command (XEP-0030)

- Add 8 tests for disco info and disco items commands
- Fix XEP-0030 compliance bug: show message for empty disco#items results
- Tests cover: identity display, features, server/jid queries, error handling,
  items display, empty results, and connection requirement

tests/functionaltests/proftest.c

@@ -362,7 +362,6 @@ close_prof_test(void **state)
         fd = 0;
         child_pid = 0;
     }
-    _cleanup_dirs();
 
     if (config_orig) {
         setenv("XDG_CONFIG_HOME", config_orig, 1);