Move flake8 option from run_tests.sh to tox.ini
Move flake8 option from run_tests.sh to tox.ini

flake8 will read the section [flake8] of tox.ini to guide the behavior.
In run_tests.sh, there is no need to add flake8 option in run_flake8()
function.

Bug #1214175

Change-Id: If3b84a0a3eecc1a9800fed6be9b24e648c161280

sdpp/python-keystoneclient,magic0704/python-keystoneclient,darren-wang/ksc,Mercador/python-keystoneclient,magic0704/python-keystoneclient,citrix-openstack-build/python-keystoneclient,metacloud/python-keystoneclient,citrix-openstack-build/python-keystoneclient,jamielennox/python-keystoneclient,ntt-sic/python-keystoneclient,citrix-openstack-build/python-keystoneclient,alexpilotti/python-keystoneclient,jamielennox/python-keystoneclient,ging/python-keystoneclient,jamielennox/python-keystoneclient,metacloud/python-keystoneclient,ntt-sic/python-keystoneclient,sdpp/python-keystoneclient,ntt-sic/python-keystoneclient,darren-wang/ksc,klmitch/python-keystoneclient,Mercador/python-keystoneclient,alexpilotti/python-keystoneclient,ging/python-keystoneclient,klmitch/python-keystoneclient