show the pf file contents in error messages for debugging

Change-Id: Ifdfbb0bb8c30a42e9384b65f93c476a69e6bd5c9
fix flake8 errors

Change-Id: Ib815badc53a22918cf7df6f505f33eae5590051e
Merge pull request #45 from dhellmann/more-pf-error-reporting

show the pf file contents in error messages for debugging
Prevent pf rules for mixed IP version floating IPs.