Fix bad mox usage.

1) No code should access mox.MoxTestCase.  We have cros_test_lib.MoxTestCase
 for this; it works and protects the environment from mox (even when tests
 fail).
2) No code should *ever* instantiate mox.Mox() directly itself; each instance
 that was, wasn't doing tear down, meaning random failures due to mocks
 being left in place.

BUG=None
TEST=unittests still work.

Change-Id: I54417c28176faf4285bc76ba66f85a8ed87e5363
Reviewed-on: https://gerrit.chromium.org/gerrit/37162
Commit-Ready: Brian Harring <ferringb@chromium.org>
Tested-by: Brian Harring <ferringb@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
diff --git a/scripts/upload_prebuilts_unittest.py b/scripts/upload_prebuilts_unittest.py
index 37c5175..1232428 100755
--- a/scripts/upload_prebuilts_unittest.py
+++ b/scripts/upload_prebuilts_unittest.py
@@ -237,13 +237,12 @@
     self.assertEqual(f.read(), '')
 
 
-class TestUploadPrebuilt(cros_test_lib.TestCase):
+class TestUploadPrebuilt(cros_test_lib.MoxTestCase):
 
   def setUp(self):
     class MockTemporaryFile(object):
       def __init__(self, name):
         self.name = name
-    self.mox = mox.Mox()
     self.pkgindex = SimplePackageIndex()
     self.mox.StubOutWithMock(binpkg, 'GrabLocalPackageIndex')
     binpkg.GrabLocalPackageIndex('/packages').AndReturn(self.pkgindex)