image/fake: added teardown method

Unit tests may alter images in FakeImageService which has pre-defined images.
Since some unit tests depend on those images, so it needs to be cleaned up
after image alternation. Otherwise running many unit tests may fail.

nova/test.py

@@ -31,6 +31,7 @@ import unittest
 
 import mox
 import nose.plugins.skip
+import nova.image.fake
 import shutil
 import stubout
 from eventlet import greenthread
@@ -119,6 +120,9 @@ class TestCase(unittest.TestCase):
                 if hasattr(fake.FakeConnection, '_instance'):
                     del fake.FakeConnection._instance
 
+            if FLAGS.image_service == 'nova.image.fake.FakeImageService':
+                nova.image.fake.FakeImageService_reset()
+
             # Reset any overriden flags
             self.reset_flags()