Ensure all working directory changes are Paths

[t00sa]

The Tool.run() method has the following signature:

def run(self,
        additional_parameters: Optional[
            Union[str, Sequence[Union[Path, str]]]] = None,
        profile: Optional[str] = None,
        env: Optional[Dict[str, str]] = None,
        cwd: Optional[Union[Path, str]] = None,
        capture_output=True) -> str:

It would be cleaner if the caller was required to ensure cwd was a Path instance. This would also allow the FabCommandError exception constructor to be cleaned up.