node check: accept -S/--superuser option

This is mainly useful for the --data-directory-config option, which
requires permission to read pg_settings to verify that the data
directory configured in "repmgr.conf" matches the data directory
actually in use.

If pg_settings read permission is not available, repmgr will fall
back to a simple check that the data directory configured in
"repmgr.conf" is a valid PostgreSQL directory. This is not entirely
foolproof, as it's possible PostgreSQL could be using a different
data directory.

repmgr-client.c

@@ -1691,6 +1691,7 @@ check_cli_parameters(const int action)
 		switch (action)
 		{
 			case STANDBY_CLONE:
+			case NODE_CHECK:
 				break;
 			default:
 				item_list_append_format(&cli_warnings,