1. Fix bug in test builds that was causing failures for some reason I
still don't understand.
`tee` output to stderr was failing with "resource temporarily
unavailable". The hack that fixed it was to simply write the herb
output to a file and dump it to stdout after it fully completes.
2. sh/cachix works without CACHIX keys. Simply doesn't upload in that case.
3. Write code to cache testbus builds (disabled for now)
4. fakeship builds get further in bootstrap sequence before committing.
This fixes problems with PRs from forked repos and enables the scripts
to be run locally.
