tests python krb5: PEP8 cleanups

tests python krb5: PEP8 cleanups

Fix all the PEP8 warnings in samba/tests/krb5. With the exception of
rfc4120_pyasn1.py, which is generated from rfc4120.asn1.

As these tests are new, it makes sense to ensure that they conform to
PEP8. And set an aspirational goal for the rest of our python code.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Gary Lockyer <gary@samba.org>
Autobuild-Date(master): Mon Dec 21 21:29:28 UTC 2020 on sn-devel-184