wrap dict with list() in for loop

In python 3, if the dict is changed in the loop, there will be
following error:
RuntimeError: dictionary changed size during iteration

Tranfrom dict with list() to fix it.

Partial implements: blueprint py33-support

Change-Id: I4b9f5bc083ebe62739a33674d26728d4a8f1a2d6

troveclient/openstack/common/apiclient/exceptions.py

@@ -392,7 +392,7 @@ class HttpVersionNotSupported(HttpServerError):
 #     _code_map = dict((c.http_status, c)
 #                      for c in HttpError.__subclasses__())
 _code_map = {}
-for obj in sys.modules[__name__].__dict__.values():
+for obj in list(sys.modules[__name__].__dict__.values()):
     if isinstance(obj, type):
         try:
             http_status = obj.http_status