dcnm_vrf: Update log messages and comments (#386)

* dcnm_vrf: Update log messages and comments

This is part 1 of multiple PRs to address issue #352.

The contents of this PR do not affect functionality.  They consist of:

1. Update/Add logging messages to help understand the code flow.
2. Update some comments.
3. Update two unit tests due to difference is logged message.

* Appease pylint

pylint is complaining about a comment.  Reformatting the comment so that it doesn't resemble:

# pylint: disable=

Author: allenrobel