The issue appears to be that because the 'clean' operation might be run
while dependencies have not yet been compiled, we applied a partial app
detection mechanism with `rebar_app_disover:find_apps(..., ..., all,
...)`, which worked to parse "invalid" (unbuilt) apps, but also did not
apply overrides.

Instead, we trust the `install_deps` provider dependency by reusing the
apps as they were fully parsed _if_ they were valid, and falling back to
the `rebar_app_discover:find_apps/4` call only to cover the unreadable
ones.

This, it turns out, has the side effect of properly applying hooks when
apps are fully parsed, and fixes erlang#2862

Note that we can only clean paths safely if the discovery steps for the
apps is done with the right profile and options, which may also impact
configurations and hooks.

So rather than duplicating that, we invoke the 'as' provider. This also
opens the door on choosing a different provider (such as 'app_discover'
only) down the road if the -a option isn't given.

The selection is a bit coarse right now (it's possible a specific app is
not a dep but a top-level app), but we regardless keep basic cleaning
as a simple discovery step to avoid installing deps there.