Update vmdebootstrap patches & minor improvements
- Remove vmdebootstrap patches 01-debootstrap-dist-bts-767806 and 02-parted-grub-space-bootspace-bts-767913. Latest vmdebootstrap git master includes the required functionality.
- Update 03-roottype-btrfs-bts-741223.patch so that it will apply cleanly.
- Enable dhcp while building all image types. (Previously was enabled only for virtualbox.)
- For Beaglebone, switch boottype to ext2 and add a bootoffset. In the customize script, use dd to install the bootloader in front of the /boot partition.