rename hardware station ports with . instead of _ between model name and port name

[RussTedrake]

@jwnimmer-tri -- PTAL? Is this the new spelling?

---

This change is 

[jwnimmer-tri]

Looks good. I pulled and up-to-date dump of a sample robot hub application and confirmed.

Here's the image of that demo, for reference:

[RussTedrake]

Thanks!