blkid is not available when this function is called, so block_uuid.map is put into
the initrd, mapping block devices from /etc/crypttab to UUIDs.
This fixes a bug where udev rules were created by mistake as crypttab_contains()
returned false for devices specified by path in /etc/crypttab which resulted in
error messages during boot.
Signed-off-by: Julian Wolf <juwolf@suse.de>