It's a bit hard to debug nailgun-agent, because it
tries to send info over http somewhere and sleeps at
the beginning. So you can't run it on your desktop, for
example.
Let's add --dry-run option, to have ability to just get
and print all information.
This is a small improvement, so no bug or blueprint.
Change-Id: If7309635d40ff3263a671fddd7df20efd917097c
(cherry picked from commit c5f7deaa98)
e7bd486ec6