hooks/updatebase.GRMLBASE: make sure /proc, /sys and /dev are available on update

When using grml-live's -u option for updating the system we need
according /proc, /sys and /dev inside the chroot, otherwise
installing some packages will fail. As FAI doesn't do this in
/usr/lib/fai/updatebase for us (but just for [dir]install) we
take care of it on our own.

Closes: issue890
Signed-off-by: Michael Prokop <mika@grml.org>