maasserver.tests.test_forms_nodegroup.TestNodeGroupDefineForm.test_rejects_invalid_interface fails spuriously

[Gavin Panella]

ERROR: maasserver.tests.test_forms_nodegroup
  .TestNodeGroupDefineForm.test_rejects_invalid_interface
-------------------------------------------------------------------
_StringException: Traceback (most recent call last):
  File ".../maastesting/runtest.py", line 68, in _run_user
    result = function(*args, **kwargs)
  File ".../testtools/testcase.py", line 616, in _run_test_method
    return self._get_test_method()()
  File ".../maasserver/tests/test_forms_nodegroup.py", line 121, in
  test_rejects_invalid_interface
    self.assertFalse(form.is_valid())
  File ".../django/forms/forms.py", line 129, in is_valid
    return self.is_bound and not bool(self.errors)
  File ".../django/forms/forms.py", line 121, in errors
    self.full_clean()
  File ".../maasserver/forms.py", line 253, in full_clean
    super(APIEditMixin, self).full_clean()
  File ".../django/forms/forms.py", line 273, in full_clean
    self._clean_fields()
  File ".../django/forms/forms.py", line 291, in _clean_fields
    value = getattr(self, 'clean_%s' % name)()
  File ".../maasserver/forms.py", line 2130, in clean_interfaces
    validate_nodegroupinterface_definition(interface)
  File ".../maasserver/forms.py", line 2037, in
  validate_nodegroupinterface_definition
    if not form.is_valid():
  File ".../django/forms/forms.py", line 129, in is_valid
    return self.is_bound and not bool(self.errors)
  File ".../django/forms/forms.py", line 121, in errors
    self.full_clean()
  File ".../maasserver/forms.py", line 253, in full_clean
    super(APIEditMixin, self).full_clean()
  File ".../django/forms/forms.py", line 274, in full_clean
    self._clean_form()
  File ".../django/forms/forms.py", line 300, in _clean_form
    self.cleaned_data = self.clean()
  File ".../maasserver/forms.py", line 1834, in clean
    self.clean_dependent_ip_ranges(cleaned_data)
  File ".../maasserver/forms.py", line 1934, in
  clean_dependent_ip_ranges
    dynamic_range_low, dynamic_range_high)
  File ".../maasserver/forms.py", line 1520, in
  validate_new_dynamic_range_size
    if ip_range.version == 6:
UnboundLocalError: local variable 'ip_range' referenced before
  assignment