Before, in order to retrieve the application name, Electron's
`getName()` method was used (https://electronjs.org/docs/api/app#appgetname).
Now, instead, we also use the Atom version in order to calculate the release
channel and be able to have it on the app name (e.g `Atom Nightly`).
In these tests, we create a temporary `ATOM_HOME` to avoid cluttering
the user's real `~/.atom` folder.
Adding a symlink to the real `compile-cache` was introduced to speed up
main process tests, so that the transpilation cache could be reused.
Unfortunately, when the real `~/.atom` folder did not exist (such as on
a pristine environment on CI), it would confuse Atom, which would think
that it didn't need to re-create a `compile-cache` folder again, but
wouldn't be able to write to it because the symlink pointed to a
non-existant directory.
Main process tests were overhauled and made faster recently, so we can
safely remove this performance optimization.
