Tempest case test_dhcp_stateful_fixedips_outrange fails due to unexpected exception

R3.0.2.0 Build 52 on Liberty

Test tempest.api.network.test_dhcp_ipv6.NetworksTestDHCPv6.test_dhcp_stateful_fixedips_outrange

The test expects that an exception is raised with message "object with that identifier already exists".

But we are throwing a different message:
Details: {u'message': u'No more IP addresses available on network 28098a54-341f-4671-9f20-2791ef1d9573.', u'type': u'IpAddressGenerationFailure', u'detail': u''}

Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/tempest/api/network/test_dhcp_ipv6.py", line 324, in test_dhcp_stateful_fixedips_outrange
    'ip_address': ip}])
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 420, in assertRaises
    self.assertThat(our_callable, matcher)
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 431, in assertThat
    mismatch_error = self._matchHelper(matchee, matcher, message, verbose)
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 481, in _matchHelper
    mismatch = matcher.match(matchee)
  File "/usr/lib/python2.7/dist-packages/testtools/matchers/_exception.py", line 108, in match
    mismatch = self.exception_matcher.match(exc_info)
  File "/usr/lib/python2.7/dist-packages/testtools/matchers/_higherorder.py", line 62, in match
    mismatch = matcher.match(matchee)
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 412, in match
    reraise(*matchee)
  File "/usr/lib/python2.7/dist-packages/testtools/matchers/_exception.py", line 101, in match
    result = matchee()
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 965, in __call__
    return self._callable_object(*self._args, **self._kwargs)
  File "/usr/local/lib/python2.7/dist-packages/tempest/api/network/base.py", line 195, in create_port
    **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/tempest/lib/services/network/ports_client.py", line 22, in create_port
    return self.create_resource(uri, post_data)
  File "/usr/local/lib/python2.7/dist-packages/tempest/lib/services/network/base.py", line 60, in create_resource
    resp, body = self.post(req_uri, req_post_data)
  File "/usr/local/lib/python2.7/dist-packages/tempest/lib/common/rest_client.py", line 270, in post
    return self.request('POST', url, extra_headers, headers, body, chunked)
  File "/usr/local/lib/python2.7/dist-packages/tempest/lib/common/rest_client.py", line 664, in request
    resp, resp_body)
  File "/usr/local/lib/python2.7/dist-packages/tempest/lib/common/rest_client.py", line 777, in _error_checker
    raise exceptions.Conflict(resp_body, resp=resp)
Conflict: An object with that identifier already exists
Details: {u'message': u'No more IP addresses available on network 28098a54-341f-4671-9f20-2791ef1d9573.', u'type': u'IpAddressGenerationFailure', u'detail': u''}