Functional test broken on AppVeyor

[josephharrington]

This is probably just a race condition in the test -- I think tests run pretty slowly on AppVeyor and so might be more likely to fail when tests rely on timing. A quick glance at the test code makes me think it is susceptible to races in at least two different places.

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FAIL: test_build_completes_after_allocating_deallocating_and_reallocating_slaves_to_build (test.functional.master.test_deallocation_and_allocation_of_slaves_mid_build.TestDeallocationAndAllocationOfSlavesMidBuild)
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Traceback (most recent call last):
  File "C:\projects\clusterrunner\test\functional\master\test_deallocation_and_allocation_of_slaves_mid_build.py", line 30, in test_build_completes_after_allocating_deallocating_and_reallocating_slaves_to_build
    self.assert_build_has_successful_status(build_id)
  File "C:\projects\clusterrunner\test\framework\functional\base_functional_test_case.py", line 106, in assert_build_has_successful_status
    self.assert_build_status_contains_expected_data(build_id, expected_successful_build_params)
  File "C:\projects\clusterrunner\test\framework\functional\base_functional_test_case.py", line 92, in assert_build_status_contains_expected_data
    'Build status API response should contain the expected status data.')
nose.proxy.AssertionError: Mismatched values: 'result', expected: 'NO_FAILURES', actual: None,'status', expected: 'FINISHED', actual: 'BUILDING' : Build status API response should contain the expected status data.
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[2017-05-19 07:12:41.699] 2076 NOTICE  MainThread      functional_test Hard killing process with pid 2844...
[2017-05-19 07:13:02.944] 2076 NOTICE  MainThread      functional_test Gracefully killing process with pid 2152...
[2017-05-19 07:13:02.944] 2076 NOTICE  MainThread      functional_test Gracefully killing process with pid 2908...
--------------------- >> end captured stdout << ----------------------