Fix test flakiness of the test test_dictionaries_update_and_reload/test_reload_after_loading

Cherry picked from https://github.com/ClickHouse/ClickHouse/pull/14958 (partly)

tests/integration/test_dictionaries_update_and_reload/test.py

@@ -186,8 +186,6 @@ def test_reload_after_fail_by_system_reload(started_cluster):
 
 
 def test_reload_after_fail_by_timer(started_cluster):
-    query = instance.query
-
     # dictionaries_lazy_load == false, so this dictionary is not loaded.
     assert get_status("no_file_2") == "NOT_LOADED"
 
@@ -204,14 +202,18 @@ def test_reload_after_fail_by_timer(started_cluster):
     # Creating the file source makes the dictionary able to load.
     instance.copy_file_to_container(os.path.join(SCRIPT_DIR, "configs/dictionaries/file.txt"),
                                     "/etc/clickhouse-server/config.d/no_file_2.txt")
-    time.sleep(6);
-    query("SELECT dictGetInt32('no_file_2', 'a', toUInt64(9))") == "10\n"
+    # Check that file appears in container and wait if needed.
+    while not instance.file_exists("/etc/clickhouse-server/config.d/no_file_2.txt"):
+        time.sleep(1)
+    assert("9\t10\n" == instance.exec_in_container("cat /etc/clickhouse-server/config.d/no_file_2.txt"))
+    instance.query("SYSTEM RELOAD DICTIONARY no_file_2")
+    instance.query("SELECT dictGetInt32('no_file_2', 'a', toUInt64(9))") == "10\n"
     assert get_status("no_file_2") == "LOADED"
 
     # Removing the file source should not spoil the loaded dictionary.
     instance.exec_in_container("rm /etc/clickhouse-server/config.d/no_file_2.txt")
     time.sleep(6);
-    query("SELECT dictGetInt32('no_file_2', 'a', toUInt64(9))") == "10\n"
+    instance.query("SELECT dictGetInt32('no_file_2', 'a', toUInt64(9))") == "10\n"
     assert get_status("no_file_2") == "LOADED"