Fix dict.keys() compatibility for python 3

In Python 2, dict.keys() will return a list.
But in Python 3, it will return an iterator.
So we need to fix all the places that assuming
dict.keys() is a list.

Change-Id: I8d1cc536377b3e5c644cfaa0892e40d0bd7c11b1
Closes-Bug: #1556350

openstackclient/shell.py

@@ -355,7 +355,7 @@ class OpenStackShell(app.App):
                         self.log.warning(
                             "%s version %s is not in supported versions %s"
                             % (api, version_opt,
-                               ', '.join(mod.API_VERSIONS.keys())))
+                               ', '.join(list(mod.API_VERSIONS.keys()))))
 
                 # Command groups deal only with major versions
                 version = '.v' + version_opt.replace('.', '_').split('_')[0]