Replace python-krbV kerberos library dependency - it is unmaintained and doesn't build on my machine any more

From the author, Michael Bonnet at Redhat:

```
python-krbV is a very old codebase, is essentially unmaintained, and isn't going to be ported
to python 3. I recommend looking into python-gssapi or python-kerberos for your use-cases:

https://pypi.org/project/gssapi/
https://pypi.org/project/kerberos/
```