Update ReSizeSteam.next() to ReSizeSteam__next__()

1. The bug.
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/opt/stack/freezer/freezer/tests/unit/openstack/test_backup.py", line 37, in test_backup_cinder_by_glance
    self.bakup_os.backup_cinder_by_glance(35)

      File "/opt/stack/freezer/freezer/openstack/backup.py", line 79, in backup_cinder_by_glance
    self.storage.add_stream(stream, package, headers=headers)

      File "/opt/stack/freezer/freezer/storage/swift.py", line 163, in add_stream
    for el in stream:

    TypeError: iter() returned non-iterator of type 'ReSizeStream'
2. Fix
In python3.x , a iterator object should be difined two funs " __iter__()" and "__next__()".

Update ReSizeSteam.next() to ReSizeSteam.__next__().

Change-Id: I940841b94789d024d3b9447f96158963fe3e16ee

freezer/tests/unit/openstack/test_backup.py

@@ -14,8 +14,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 
 """
-import sys
-import unittest
 
 from freezer.openstack import backup
 from freezer.tests import commons
@@ -31,8 +29,6 @@ class TestBackup(commons.FreezerBaseTestCase):
         self.client_manager = self.backup_opt.client_manager
         self.storage = self.backup_opt.storage
 
-    @unittest.skipIf(sys.version_info.major == 3,
-                     'Not supported on python v 3.x')
     def test_backup_cinder_by_glance(self):
         self.bakup_os.backup_cinder_by_glance(35)
 

freezer/utils/utils.py

@@ -263,7 +263,7 @@ class ReSizeStream(object):
     def __iter__(self):
         return self
 
-    def next(self):
+    def __next__(self):
         LOG.debug("Transmitted {0} of {1}".format(self.transmitted,
                                                   self.length))
         chunk_size = self.chunk_size