Creating campaign actions causes jittery progress updates when a lot of repos are involved

[nicksnyder]

The video doesn't really capture all the jitteryness, perhaps due to recoding framerate.: https://p-YvFVk4.t1.n0.cdn.getcloudapp.com/items/E0uz8X92/Screen%20Recording%202020-06-09%20at%2011.42%20AM.mp4

[nicksnyder]

I would rather see output streamed (e.g. when a repo is done, emit a line)

[mrnugget]

Duplicate of #118.

@nicksnyder regarding the "one line per repo": try src -v action exec, note the -v. I'm wondering whether we shouldn't make that the default.