Handle StopIteration for Py3.7

Catch the raise of StopIteration with return.

PEP 0479, https://www.python.org/dev/peps/pep-0479/, makes the
following change: "when StopIteration is raised inside a generator,
it is replaced it with RuntimeError".
And states: "If raise StopIteration occurs directly in a generator,
simply replace it with return."

Closes-Bug: #1785309
Change-Id: Ib751b680b7357782cb5359526e1e83ee8c5c80dd

zunclient/common/httpclient.py

@@ -395,7 +395,10 @@ class ResponseBodyIterator(object):
 
     def __iter__(self):
         while True:
-            yield self.next()
+            try:
+                yield self.next()
+            except StopIteration:
+                return
 
     def next(self):
         chunk = self.resp.read(CHUNKSIZE)