Otherwise, `System.console() == null`.

1. Migrate to `NuProcess` and avoid the annoying Java and Scala process
APIs. Nuprocess gives us a better foundation to deal with stdout and
stderr, as well as processing standard input from the host process
(Bloop). `NuProcess` will also be more efficient than our previous
approach.

2. Migrate test server and the whole `runMain` machinery to `Task` so
that we can have a finer control over it. Note that now these actions
can be cancelled!

It fails spuriously with good reason: Bloop doesn't yet support
concurrent clients. When we do, we'll re-enable this test suite.

The modernization makes sure that:

1. All processes that call bloop do provide an empty or inherited input
stream in both the server part and the client part.

2. The implementation is task based so that we can remove the annoying
thread sleep + have automatic shutdown of the processes if the timeout
is not met.

I think this is one of the reasons why our nailgun-based test infrastructure has been traditionally not very stable. Let's see if this fixes it.