Ensure ros2doctor ROS nodes have valid names.

[hidmic]

Precisely what the title says. Came across this while testing ros2 doctor hello on a VM that had dashes in its hostname. It's tricky one to test for regression, so I'm open to ideas.

[claireyywang]

LGTM! I think as long as we can enforce node name uniqueness this should be fine

[jacobperron]

For a test, we could try using mock as described in this SO answer.

[hidmic]

@claireyywang @jacobperron PTAL. I changed tests' layout a bit as the existing ones where not testing anything. I'd think there was some confusion w.r.t pytest vs. unittest and their relationship w/ launch_testing.

On a side note, I find the hello verb implementation rather unusual. Particularly when it starts spawning short-lived daemon threads in a loop. IMHO a pool of threads would be cheaper and provide for tighter thread lifetime control.

[jacobperron]

I'd think there was some confusion w.r.t pytest vs. unittest and their relationship w/ launch_testing.

Oof, I didn't realize that. I wonder if there are other places in our code base that make a similar mistake.

[jacobperron]

LGTM with green CI

[hidmic]

CI up to ros2doctor:

• Linux
• Linux-aarch64
• macOS
• Windows

[hidmic]

Focal PR job failure is unrelated. Have two approvals. Merging.