Remove useless test for the CooperativeReader class

test_cooperative_reader_of_iterator_stop_iteration_err passes an empty
list to utils.CooperativeReader since "[l * 3 for l in '']" evaluates to
an empty list. The
test_cooperative_reader_unbounded_read_on_empty_iterator also
initializes utils.CooperativeReader this way.

The function's docstring is a copy/paste of
test_cooperative_reader_of_iterator's.  Judging by the method's name, it
seems its goal was to make sure the StopIteration exception was properly
handled in CooperativeReader.read(), which is already tested by the
following methods:

- test_cooperative_reader_of_iterator
- test_cooperative_reader_on_iterator_with_buffer
- test_cooperative_reader_unbounded_read_on_iterator
- test_cooperative_reader_preserves_size_chunk_equals_read
- test_cooperative_reader_preserves_size_chunk_less_then_read
- test_cooperative_reader_preserves_size_chunk_more_then_read
- test_cooperative_reader_unbounded_read_on_empty_iterator

The test_cooperative_reader_of_iterator_stop_iteration_err therefore
seems useless and is removed in this commit.

Change-Id: I28834aab2602f59cbfa3ba061ab245af7ac56c40

glance/tests/unit/common/test_utils.py

@@ -221,17 +221,6 @@ class TestUtils(test_utils.BaseTestCase):
         reader = utils.CooperativeReader([])
         self.assertEqual(b'', reader.read())
 
-    def test_cooperative_reader_of_iterator_stop_iteration_err(self):
-        """Ensure cooperative reader supports iterator backends too"""
-        reader = utils.CooperativeReader([l * 3 for l in ''])
-        chunks = []
-        while True:
-            chunks.append(reader.read(3))
-            if chunks[-1] == b'':
-                break
-        meat = b''.join(chunks)
-        self.assertEqual(b'', meat)
-
     def _create_generator(self, chunk_size, max_iterations):
         chars = b'abc'
         iteration = 0