Queens: update flake8 to 2.6
Queens: update flake8 to 2.6

Introduces pycodestyle dependency (replacement to pep8)
This is required for https://review.rdoproject.org/r/#/c/11379/

Change-Id: I2706947042e74c64f4e5215f579246c989ac93cc

redhat-openstack/rdoinfo,javierpena/rdoinfo