Add pyflakes to test-requires
Add pyflakes to test-requires

pyflakes needs to be installed in the venv

Change-Id: Ie7aada13da4e191108363c80daf719212d06d316
Fixes: Bug #1131275

dims/heat,Triv90/Heat,JioCloud/heat,gonzolino/heat,openstack/heat,pratikmallya/heat,noironetworks/heat,cryptickp/heat,citrix-openstack-build/heat,varunarya10/heat,openstack/heat,dims/heat,miguelgrinberg/heat,jasondunsmore/heat,Triv90/Heat,maestro-hybrid-cloud/heat,noironetworks/heat,jasondunsmore/heat,steveb/heat,rickerc/heat_audit,Triv90/Heat,ntt-sic/heat,gonzolino/heat,pshchelo/heat,srznew/heat,srznew/heat,takeshineshiro/heat,rdo-management/heat,dragorosson/heat,rdo-management/heat,redhat-openstack/heat,maestro-hybrid-cloud/heat,ntt-sic/heat,steveb/heat,cryptickp/heat,rickerc/heat_audit,NeCTAR-RC/heat,miguelgrinberg/heat,redhat-openstack/heat,rh-s/heat,pratikmallya/heat,cwolferh/heat-scratch,pshchelo/heat,JioCloud/heat,rh-s/heat,cwolferh/heat-scratch,dragorosson/heat,takeshineshiro/heat,citrix-openstack-build/heat,NeCTAR-RC/heat,varunarya10/heat