Build History for pull/180

Overlayfs backend

Rather than build in the `results` directory, the builds now happen in the `in-progress` directory. This is necessary as, without it, interupted builds appear in the result directory and the `get_build` function in lib/db_store.ml assumes that there is valid build based only on the existence of the output directory (it does not query the database).

exec rather than sudo

Fix and update workflow

Overlayfs backend