Tempest jobs fail with TypeError: tuple indices must be integers, not str

[Dmitry Tantsur]

Example: http://logs.openstack.org/58/96558/22/check/check-tempest-dsvm-virtual-ironic/0a7d618/logs/testr_results.html.gz

Traceback (most recent call last):
  File "tempest/api/baremetal/test_ports_negative.py", line 25, in setUp
    chassis = self.create_chassis()['chassis']
TypeError: tuple indices must be integers, not str