Amend unused variables to assist pylint testing

Amedning unused variables with a prefix of an underscore to prevent them
being picked up in pylint testing, consistency, and for general housekeeping.
Change to pylintrc also required to enforce the rule.

Closes-bug #1268062

Change-Id: I80c2cbdc52d6f37823fae90d0096836166412643
Merge "Amend unused variables to assist pylint testing"