Periodic test failure for compose_curtin_network_preseed_for

The following test fails periodically:

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FAIL: maasserver.tests.test_networking_preseed.TestComposeCurtinNetworkPreseedFor.test__composes_config
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_StringException: Traceback (most recent call last):
  File "/home/blake/Code/handle-poweroff-purpose/src/maasserver/tests/test_networking_preseed.py", line 797, in test__composes_config
    self.assertThat(fake, MockCalledOnceWith(node, expected_config))
  File "/usr/lib/python2.7/dist-packages/testtools/testcase.py", line 406, in assertThat
    raise mismatch_error
MismatchError: Expected call: mock(<Node: node-a99f6e1e-4eb4-11e4-b07c-0026bb1cd6ae (XQGNlxB8eeGCg4qzOCVn)>, {u'nameservers': ['95.164.126.127'], u'interfaces': [5b:e3:87:04:80:43], u'gateways_mapping': {5b:e3:87:04:80:43: ['95.164.126.48']}, u'ips_mapping': {}, u'auto_interfaces': [5b:e3:87:04:80:43]})
Actual call: mock(<Node: node-a99f6e1e-4eb4-11e4-b07c-0026bb1cd6ae (XQGNlxB8eeGCg4qzOCVn)>, {u'nameservers': [], u'interfaces': [5b:e3:87:04:80:43], u'gateways_mapping': {u'5b:e3:87:04:80:43': [u'95.164.126.48']}, u'ips_mapping': {}, u'auto_interfaces': [u'5b:e3:87:04:80:43']})