Pin pep8 to 1.3.3

Part of making pep8 version standard across all openstack
projects.

Fixes LP: #1143569

Change-Id: Iefc923123243df161ed72888c1651a622afbda04
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "Pin pep8 to 1.3.3"