Enabled F821, H306, H402, and H404 flake8 rule

Reasons:
- F821 is disabled.
- H306 is disabled.
- H402 is disabled.
- H404 is disabled.

Changes:
- Updates tox.ini to enable F821, H306, H402 and H404 rules.
- Updates code for F821, H306, H402 and H404 violation.

Change-Id: I772270bb833ac774e080fc63e330d6b333f23de2
Merge "Enabled F821, H306, H402, and H404 flake8 rule"