Makefile: Pack squashfs and f2fs tools into otatools.zip.

The following tools are essential to create squashfs and f2fs images
during signing (if applicable).

squashfs: mksquashfs and mksquashfsimage.sh
f2fs: make_f2fs and mkf2fsuserimg.sh

Bug: 28179154
Change-Id: Ia48bc6d9a40d2667bc6f2c973bd0c55eed7a06fc