cifs: Add support for failover in cifs_mount()

This patch adds support for failover when failing to connect in
cifs_mount().

Signed-off-by: Paulo Alcantara <palcantara@suse.de>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>