Using set -e in all of our scripts will prevent some subtle bugs
from slipping in, and will allow us to enforce use of set -e with
tooling.
This change also adds -u and set -o pipefail in the less complex
scripts where it is unlikely to cause problems. A follow-up change
will enable those options in the complex scripts so that if it
breaks something it can be reverted easily.
Change-Id: I0ad358ccb98da7277a0ee2e9ce8fda98438675eb
Many python extensions are built from source each time an image is
built. Repeating these is wasteful, so ccache is employed to eliminate
that waste. A cache dir outside the chroot is used to speed up
subsequent image builds.
Change-Id: Ib73563ddbe5f3be7454bfc54ab91cedb559a1304
