dump_logs routine in test framework is fragile

[Pen Gale]

Host.dump_logs is fragile. It breaks, for example, if we weren't able to install the snap, and don't have snap log dirs.

I've commented it out from the testing framework for now. (We get a lot of what we need from the captured stdout, or local testing, anyway.)

We need to loop back and make dump_logs better. Possibly by just grabbing the `systemctl status snap.microstack.* --no-pager` and `journalctl -xe --no-pager`, instead of trying to round up stray logs in the snap common dir.