Global west state makes it harder to unit test

[mbolivar]

West has some global state that makes it harder to write proper unit tests. Examples:

• global configuration state is written into a module-level object in west.config
• log verbosity level is too

This makes it harder to write proper unit tests and causes other annoyances.

---

2024 update:

We're down to west.log at this point. We can close this issue once that deprecated module is removed sometime in the west 2.0 or later timeline.

[mbolivar]

This bugs me all the time when I write tests, and I'm constantly having to hack around it, as shown in #271. Bumping priority to medium as a result (since it's a problem that is slowing down development, despite not being user-visible).