Enables E711,E721,E712 pep8 rules

Updates tox.ini to reduce ignored rules.

Updates novaclient/v1_1/shell.py and
novaclient/v3/shell.py for E712 violation.

Change-Id: Ibfd6a4ed19835e65cc9e27873699c31a801e99a8
Merge "Enables E711,E721,E712 pep8 rules"