thin-provisioning-tools needs an initramfs-tools hook to support booting into a rootfs stored in a thin pool

The boot process stalls within the generated ramfs images on 16.04 when the rootfs exists within a thin pool due to a missing /usr/sbin/thin_check. I've attached an initramfs hook script which pulls in all of the module and library dependencies in addition to the /usr/sbin/pdata_tools binary and its thin_* symlinks. So far, it has been tested and found to fix the problem on 16.04(.1) on both the x86_64 and arm architectures, but I see no reason why it wouldn't work anywhere else where the thin-provisioning-tools package exists and fails to provide anything similar.