Unit test test_validate_patternProperties_fails fails under Python 3.6

[Thomas Goirand]

Running unit tests under Python 3.6 fails while working in Python 2.7:

cinder.tests.unit.api.test_api_validation.PatternPropertiesTestCase.test_validate_patternProperties_fails
---------------------------------------------------------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b' File "/home/zigo/sources/openstack/queens/services/cinder/build-area/cinder-12.0.0~rc1/cinder/api/validation/validators.py", line 208, in validate'
    b' self.validator.validate(*args, **kwargs)'
    b' File "/usr/lib/python3/dist-packages/jsonschema/validators.py", line 129, in validate'
    b' for error in self.iter_errors(*args, **kwargs):'
    b' File "/usr/lib/python3/dist-packages/jsonschema/validators.py", line 105, in iter_errors'
    b' for error in errors:'
    b' File "/usr/lib/python3/dist-packages/jsonschema/_validators.py", line 14, in patternProperties'
    b' if re.search(pattern, k):'
    b' File "/usr/lib/python3.6/re.py", line 182, in search'
    b' return _compile(pattern, flags).search(string)'
    b'TypeError: expected string or bytes-like object'
    b''
    b'During handling of the above exception, another exception occurred:'
    b''
    b'Traceback (most recent call last):'
    b' File "/home/zigo/sources/openstack/queens/services/cinder/build-area/cinder-12.0.0~rc1/cinder/tests/unit/api/test_api_validation.py", line 95, in check_validation_error'
    b' method(body=body, req=req,)'
    b' File "/home/zigo/sources/openstack/queens/services/cinder/build-area/cinder-12.0.0~rc1/cinder/api/validation/__init__.py", line 59, in wrapper'
    b" schema_validator.validate(kwargs['body'])"
    b' File "/home/zigo/sources/openstack/queens/services/cinder/build-area/cinder-12.0.0~rc1/cinder/api/validation/validators.py", line 225, in validate'
    b' raise exception.ValidationError(detail=detail)'
    b'cinder.exception.ValidationError: expected string or bytes-like object'
    b''
    b'During handling of the above exception, another exception occurred:'
    b''
    b'Traceback (most recent call last):'
    b' File "/home/zigo/sources/openstack/queens/services/cinder/build-area/cinder-12.0.0~rc1/cinder/tests/unit/api/test_api_validation.py", line 247, in test_validate_patternProperties_fails'
    b' expected_detail=detail)'
    b' File "/home/zigo/sources/openstack/queens/services/cinder/build-area/cinder-12.0.0~rc1/cinder/tests/unit/api/test_api_validation.py", line 103, in check_validation_error'
    b" 'Exception details did not match expected')"
    b' File "/usr/lib/python3/dist-packages/testtools/testcase.py", line 411, in assertEqual'
    b' self.assertThat(observed, matcher, message)'
    b' File "/usr/lib/python3/dist-packages/testtools/testcase.py", line 498, in assertThat'
    b' raise mismatch_error'
    b"testtools.matchers._impl.MismatchError: 'expected string or buffer' != 'expected string or bytes-like object': Exception details did not match expected"