When the 'loop' kernel module isn't loaded in a running system, it gets
excluded from the hostonly initrd. Given that the crypt-loop dracut
module has to be loaded explicitly anyway, it makes sense to always
include the requisite loop kernel module.
Add new functions require_binaries() and require_any_binary() to be used
in the check() section of module-setup.sh.
These functions print a warning line telling the user, which binary is
missing for the specific dracut module.
This unifies the way of checking for binaries and makes the life of an
initramfs creator easier, if he wants to find out why a specific dracut
module is not included in the initramfs.
James Lee