nixos-rebuild test causes pam_mount to prompt for a password when running with
an encrypted home:
building '/nix/store/p6bflh7n5zy2dql8l45mix9qnzq65hbk-nixos-system-mildred-18.09.git.98592c5da79M.drv'...
activating the configuration...
setting up /etc...
reenter password for pam_mount:
(mount.c:68): Messages from underlying mount program:
(mount.c:72): crypt_activate_by_passphrase: File exists
(pam_mount.c:522): mount of /dev/mapper/vg0-lv_home_peter failed
kbuildsycoca5 running...
This change makes pam_mount not prompt. It still tries to remount (and fails in
the process) but that message can be ignored.
Fixes: #44586
22a500a3f8