If no password in env or command line, try prompting

Implements keystone portion of blueprint prompt-for-password

For security reasons, having the password on the command line
or in the environment is an issue for us. (See the blueprint for
details.) This change will simply make one attempt to prompt for
a password if (1) nothing was specified already and (2) there's
a tty available for the user to respond on. If we don't get a
password, then the existing error will be raised.

Remoted getpass from pip-requires, it's in the std lib

Tweaked a comment

Tweaked error message

Don't catch Ctl-C

Fix import to match conventions

Missed a tweak during the rebase.

Added suggested password prompt

Change-Id: I54bca2397da7bd366f7ac503e767b109efc093e7

keystoneclient/shell.py

@@ -19,6 +19,7 @@ Command-line interface to the OpenStack Identity API.
 """
 
 import argparse
+import getpass
 import httplib2
 import os
 import sys
@@ -282,10 +283,21 @@ class OpenStackIdentityShell(object):
                         'Expecting a username provided via either '
                         '--os-username or env[OS_USERNAME]')
 
+                if not args.os_password:
+                    # No password, If we've got a tty, try prompting for it
+                    if hasattr(sys.stdin, 'isatty') and sys.stdin.isatty():
+                        # Check for Ctl-D
+                        try:
+                            args.os_password = getpass.getpass('OS Password: ')
+                        except EOFError:
+                            pass
+                    # No password because we did't have a tty or the
+                    # user Ctl-D when prompted?
                     if not args.os_password:
                         raise exc.CommandError(
                             'Expecting a password provided via either '
-                        '--os-password or env[OS_PASSWORD]')
+                            '--os-password, env[OS_PASSWORD], or '
+                            'prompted response')
 
                 if not args.os_auth_url:
                     raise exc.CommandError(