teuthology/run_tasks.py: drop six.ensure_str()
teuthology/run_tasks.py: drop six.ensure_str()

Signed-off-by: Kefu Chai <a4b264ee037c625052534d60505bfd0db4776ac4@redhat.com>

SUSE/teuthology,ktdreyer/teuthology,dmick/teuthology,dmick/teuthology,ceph/teuthology,SUSE/teuthology,ktdreyer/teuthology,SUSE/teuthology,ceph/teuthology,dmick/teuthology