Issue a message when a configuration file is passed unnecessarily

Simply intends to set expectations around the fact that a config file
is not used *and* doesn't affect anything material about the standby
clone command.

This uses a notion of "logging level" (like NOTICE) that is not yet
seen this program, but I'll probably introduce that soon.

Signed-off-by: Daniel Farina <daniel@heroku.com>

repmgr.c

@@ -1558,6 +1558,16 @@ check_parameters_for_action(const int action)
 		}
 		break;
 		case STANDBY_CLONE:
+			/*
+			 * Issue a friendly notice that the configuration file is not
+			 * necessary nor read at all in when performing a STANDBY CLONE
+			 * action.
+			 */
+			if (config_file != NULL)
+				fprintf(stderr, "NOTICE: The passed configuration file is not "
+						"required nor used when performing the STANDBY CLONE "
+						"command.\n");
+
 			/*
 			 * To clone a master into a standby we need connection parameters
 			 * repmgr.conf is useless because we don't have a server running in