We added the `--all` flag (now renamed to `--eval-all`) for various
commands for this behaviour so let's start deprecating this.
Also, introduce a `HOMEBREW_EVAL_ALL` environment variable to use the
existing, less secure, behaviour by default and avoid passing
`--eval-all` everywhere.
This makes use of both the existing interfaces and could use the
existing cache file but we'll create a new one and cleanup the old one
to avoid issues and use a more consistent name.
We have an awful lot of integration tests and they are (comparatively)
really slow. Let's kill those that test edge case conditions and focus
on those that test that our functionality works as expected. Edge cases
can be better tested with unit tests.
