cmdeploy: allow to run SSH commands locally

[missytake]

fix #604
related to #629
pulled out of Keonik1#3

[missytake]

I disabled parts of this test; cmdeploy dns works as expected, but capsys.readouterr() fails to capture what log_progress() writes to sys.stderr. It looks related to https://stackoverflow.com/a/29567317

It's weird because capturing what print_stderr() posts to sys.stderr works. But we can't put log_progress() in sshexec.py, because then we can't import it in remote/rdns.py, as it is outside of the remote module, and from cmdeploy.sshexec import log_progress somehow doesn't work.

It's messy, and before I waste another hour with this I'd rather disable this in the test; it's just checking whether the output is pretty, after all, nothing critical. But if anyone has an idea what is going wrong, feel free to contribute.

What could also help is dropping remote as a separate python module. That would anyway help with code structure, right now it is spread out over many files. But by now, I understand only half of what's going on there, so someone else would need to do this.