[Samba] When ad domain machine shutdown, samba can not auth with unix local user

[谷雷]

Hi,
	I config my samba join a ad domain(security = ADS), using samba 4.7.1 in CentOS7.5.

	Everything gone well, I can login with ad user and local user at the same time.

	But when the ad domain get down, I can not login with local user.

	wbinfo -t prompt: NT_STATUS_DOMAIN_CONTROLLER_NOT_FOUND,
	smbclient login with NT_STATUS_NO_LOGON_SERVER error.

	I lookup the debug message, and found auth method winbind break in auth_check_ntlm_password, 
	and not try sam_ignoredomain method.

	May there some way make samba can auth with unix local when ad domain get down?