Pass prompt_for_password to OSC_Config constructor

In order to remove the OSC_Config from python-openstackclient, we need
to plumb the pw_func pieces through to the OSC_Config here. (we can
address removing OSC_Config from osc-lib later) Without doing this, the
logic in osc_lib/cli/client_config.py won't work because
self._pw_callback won't be set.

Change-Id: I16cb906983ea4036b958ed67ebfd042cf8e5aaf1

osc_lib/shell.py

@@ -407,6 +407,7 @@ class OpenStackShell(app.App):
         # will it be used.
         try:
             self.cloud_config = cloud_config.OSC_Config(
+                pw_func=prompt_for_password,
                 override_defaults={
                     'interface': None,
                     'auth_type': self._auth_type,