fix(make_chroot.sh): Remove duplicate chroot toolchain setup code.

Instead of handling toolchain packages in make_chroot and telling
update_chroot to skip the toolchains just depend on update_chroot to do
it properly. Reduces our code duplication by a tiny but worthwhile bit.
fix(update_chroot): Move to new toolchain_util.sh library

Switch from cros_setup_toolchains to the new simpler toolchain_util code
for installing toolchains in the SDK chroot.
Merge pull request #136 from marineam/turtle-chain

Turtle chain