molecule tests in tripleo-validations fail

Description
===========
It appears that the molecule tests in train for tripleo-validations are failing to execute.
See https://review.opendev.org/#/c/749575/2 for details of two failing molecule tests.

This issue may be related: https://github.com/ansible-community/molecule/issues/2676

Steps to reproduce
==================
Run the molecule tests in train for tripleo-validations

Expected result
===============
Test should execute.

Actual result
=============
Tests fail to execute:

  File "/usr/lib64/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/__main__.py", line 24, in <module>
    main()
  File "/home/zuul/test-python/lib/python2.7/site-packages/click/core.py", line 829, in __call__
    return self.main(*args, **kwargs)
  File "/home/zuul/test-python/lib/python2.7/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/home/zuul/test-python/lib/python2.7/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/zuul/test-python/lib/python2.7/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/zuul/test-python/lib/python2.7/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/home/zuul/test-python/lib/python2.7/site-packages/click/decorators.py", line 21, in new_func
    return f(get_current_context(), *args, **kwargs)
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/command/test.py", line 148, in test
    base.execute_cmdline_scenarios(scenario_name, args, command_args)
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/command/base.py", line 98, in execute_cmdline_scenarios
    execute_scenario(scenario)
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/command/base.py", line 141, in execute_scenario
    execute_subcommand(scenario.config, action)
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/command/base.py", line 128, in execute_subcommand
    return command(config).execute()
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/command/destroy.py", line 104, in execute
    self._config.provisioner.destroy()
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/provisioner/ansible.py", line 680, in destroy
    pb.execute()
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/provisioner/ansible_playbook.py", line 92, in execute
    self.bake()
  File "/home/zuul/test-python/lib/python2.7/site-packages/molecule/provisioner/ansible_playbook.py", line 74, in bake
    _err=self._err
  File "/home/zuul/test-python/lib/python2.7/site-packages/sh.py", line 1367, in bake
    call_args, kwargs = self._extract_call_args(kwargs)
  File "/home/zuul/test-python/lib/python2.7/site-packages/sh.py", line 1358, in _extract_call_args
    raise TypeError("Invalid special arguments:\n\n%s\n" % exc_msg)
TypeError: Invalid special arguments:

  'env': value u'/home/zuul/src/opendev.org/openstack/tripleo-validations/roles/switch_vlans/.env.yml' of env key 'MOLECULE_ENV_FILE' must be a str

Environment
===========
Train