Downloading image with --progress fails

Downloading image with --progress fails with "RequestIdProxy object is
not an iterator". This is because to display download progress
VerboseFileWrapper in progressbar requires object of IterableWithLength,
but after support of returning request-id [1] to caller it returns
RequestIdProxy object which is wrapped around IterableWithLength
and response.

To resolve this issue overridden next and __next__ methods in
RequestIdProxy so that it can act as iterator for python 2.x
and 3.x as well.

[1] 610177a779

Closes-Bug: #1670464
Change-Id: I188e67c2487b7e4178ea246f02154bbcbc35a2b1

glanceclient/common/utils.py

@@ -494,6 +494,13 @@ class RequestIdProxy(wrapt.ObjectProxy):
     def wrapped(self):
         return self._self_wrapped
 
+    # Overriden next method to act as iterator
+    def next(self):
+        return next(self._self_wrapped)
+
+    # In Python 3, __next__() has replaced next().
+    __next__ = next
+
 
 class GeneratorProxy(wrapt.ObjectProxy):
     def __init__(self, wrapped):