pyflake8 was updated and not properly constrainted by hacking, update
to hacking 3.1.0 and fix the problems found.
py27 failed since global upper-constraints includes py3 only packages.
Use lower-constraints for this test.
The functional jobs run on master with py27, remove the py27 master job,
change the jobs so that py3 is used everywhere.
Change-Id: I695d60e53857e03f206dcd7cf10c06c76c8d6cc0
08c07018dc