Fix ./run_tests.sh --pep8
Fix ./run_tests.sh --pep8

Create a common script to call flake8 to share flake8 options and
make tox and run_tests.sh use this script.

Fixes bug: 1179331

Change-Id: I92dc54fa3f4bb22aa39bde226b6d769088f9a2e3

Tehsmash/networking-cisco,Gitweijie/first_project,Tehsmash/networking-cisco-nexus,openstack/networking-cisco,noironetworks/networking-cisco,hareeshpc/networking-cisco,openstack/networking-cisco,cisco-openstack/networking-cisco,Tehsmash/networking-cisco,noironetworks/networking-cisco,cisco-openstack/networking-cisco,CiscoSystems/networking-cisco,hareeshpc/networking-cisco,Tehsmash/networking-cisco-apic,Gitweijie/first_project,nikolay-fedotov/networking-cisco,CiscoSystems/networking-cisco