Fix auth prompt brokenness

We start by fixing this in the already-present OSC_Config class so OSC
can move forward.  This change needs to get ported down into
os-client-config in the near future, maybe even soon enough to make the
client library freeze this week.

* Add the pw-func argument to the OSC_Config (or OpenStackConfig) __init__()
* When looping through the auth options from the KSA plugin look for any
  that have a prompt defined and do not have a value already, so ask for one.

Closes-bug: #1617384
Change-Id: Ic86d56b8a6844516292fb74513712b486fec4442

openstackclient/shell.py

@@ -145,6 +145,7 @@ class OpenStackShell(shell.OpenStackShell):
                     'interface': None,
                     'auth_type': self._auth_type,
                 },
+                pw_func=shell.prompt_for_password,
             )
         except (IOError, OSError) as e:
             self.log.critical("Could not read clouds.yaml configuration file")
@@ -162,7 +163,6 @@ class OpenStackShell(shell.OpenStackShell):
         self.client_manager = clientmanager.ClientManager(
             cli_options=self.cloud,
             api_version=self.api_version,
-            pw_func=shell.prompt_for_password,
         )