Ensure that a non-zero exit code is set both for missing random dylibs
and random missing dependencies.

Additionally, while we are here, drastically trim down the public
interface for this class to the bare minimum and allow getting the
output from `display_test_output` as a variable.

Fixes issue mentioned by @ilovezfs in:
https://github.com/Homebrew/brew/pull/3940#issuecomment-383794520

No reason to have it in macOS class and keeps consistent output with
`brew info` on Linux.

Otherwise the ordering varies based on the filesystem.

The `cask` attribute doesn't make as much sense on Linux but can be
ignored there. The advantage of this change is that (like #4086) it
allows figuring out the relevant cask for a formulae requirement on a
Linux machine.

Make some changes required to have `brew info --json=v1` whether there
is any bottle block rather than a bottle checksum for the given system.

This provides more consistent output.

Fixes #4084.

It's unnecessary extra complexity to have versions that are keg-only on
some versions of macOS and not others.

Initially this was to only do so on old versions of OS X and Xcode but
the discussion in https://github.com/Homebrew/brew/pull/4081 meant that
it made more sense to remove them all.

It's safe since 600d58f4 when
MacOS::Xcode.version started returning `Version::NULL` where
appropriate.

`odisabled` will still return for a formula in `.brew`. This means
`EOS.undent` returns `nil` and the formula cannot be parsed. Instead
return the actual string in this case to avoid e.g. patches blowing up
with `nil` strings.

Fixes #4049.

* specify repository location using `-C` option
* change `newest` to `latest` when talking about the latest tagged
commit