This fixes a bunch of minor pylint warnings:
* Drop unused imports.
* Fix "inline-JSON" formatting.
* Fix space before/after brackets.
* Use `_` for unused variables.
* Break overlong lines.
* Mark unittest as `no-self-use` if applicable.
* Drop spurious newline at end of file.
Rename the function to `describe_os()`. We do no actual detection, nor
verification here. That is, the return value of this function is in no
way guaranteed to be a valid runner. That is, error-handling needs to
be done in the caller. Make this clear by renaming the function.
Note: Currently, in case no runner exists for the OS, we end up with:
execv(...) failed: No such file or directory
This needs to be fixed in the future.
