persistence luks mounting "Loading" error

loadkeys in load_keymap was outputting a message about Loading
/etc/boottime.kmap.gz and that was taken into account as return value
for open_luks_device(). loadkeys is now called with -q (quiet) switch.

This was a boot message example before the fix, notice the "mounting Loading":

    Begin: Running /scripts/live-realpremount ... done.
    Begin: Mounting "/live/medium/live/filesystem.squashfs" on "//filesystem.squashfs" via "/dev/loop0" ... done.
    Enter passphrase for /dev/sdb2:
    mount: mounting Loading on /live/persistence/Loading failed: No such device
    sort: /tmp/custom_mounts.list: No such file or directory
    /init: line 1: can't open /tmp/custom_mounts.list: no such file
    rm: can't remove '/tmp/custom_mounts.list': No such file or directory
    umount: can't umount /live/overlay: Device or resource busy
    done.
    Begin: Configuring fstab ... done.
    Begin: Preconfiguring networking ... done.