test_dehydrate_partitions_returns_list_of_partitions fails spuriously

[Gavin Panella]

ERROR: maasserver.websockets.handlers.tests.test_node
  .TestNodeHandler.test_dehydrate_partitions_returns_list_of_partitions
----------------------------------------------------------------------
_StringException: Traceback (most recent call last):
  File ".../src/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 ".../src/maasserver/websockets/handlers/tests/test_node.py", line
  395, in test_dehydrate_partitions_returns_list_of_partitions
    for _ in range(3)
  File ".../src/maasserver/testing/factory.py", line 1267, in
  make_Partition
    "Cannot make another partition on partition_table not "
ValueError: Cannot make another partition on partition_table not enough
free space.