qa: Enable flake8 tox and fix failures

qa: Enable flake8 tox and fix failures

There were a couple of problems found by flake8 in the qa/
directory (most of them fixed now). Enabling flake8 during the usual
check runs hopefully avoids adding new issues in the future.

Signed-off-by: Thomas Bechtold <tbechtold@suse.com>
(cherry picked from commit 0127cd1e8817b05b1c3150540b021f9a24b47089)

Conflicts:
	qa/tasks/barbican.py
	qa/tasks/cephadm.py
	qa/tasks/cephfs/test_cephfs_shell.py
	qa/tasks/cephfs/xfstests_dev.py
	qa/tasks/daemonwatchdog.py
	qa/tasks/mgr/dashboard/test_cephfs.py
	qa/tasks/mgr/dashboard/test_orchestrator.py
	qa/tasks/mgr/dashboard/test_rbd.py
	qa/tasks/mgr/mgr_test_case.py
	qa/tasks/mgr/test_orchestrator_cli.py
	qa/tasks/s3tests.py
	qa/tasks/s3tests_java.py
	qa/tasks/vstart_runner.py
	qa/workunits/mon/caps.py: trivial resolutions,
          and drop the the change to qa/CMakeLists.txt, as we don't have
          add_tox_test() back in nautilus