Calculate a suitable column width for positional arguments

Overwrite the method add_arguments in the class
OpenStackHelpFormatter to calculate a suitable columnt width
(max_help_position) for the positional arguments.

example output before this patch:

    ec2-credentials-create
                        Create EC2-compatible credentials for user per tenant.
    ec2-credentials-delete
                        Delete EC2-compatible credentials.
    ec2-credentials-get
                        Display EC2-compatible credentials.
    ec2-credentials-list
                        List EC2-compatible credentials for a user.

example output after this patch:

    ec2-credentials-create  Create EC2-compatible credentials for user per
                            tenant.
    ec2-credentials-delete  Delete EC2-compatible credentials.
    ec2-credentials-get     Display EC2-compatible credentials.
    ec2-credentials-list    List EC2-compatible credentials for a user.

Change-Id: Ibd5d3502022d2afcfd4f57fef9a0bbf23d34b767
Closes-Bug: #1326471
Don't log sensitive auth data

Add the ability to turn off logging from the session object and then
handle logging of auth requests within their own sections.  This is a
very simplistic ability to completely disable logging.  Logging more
filtered debugging can be added later.

This new ability is utilized in this patch to prevent logging of
requests that include passwords.  This covers authenticate, password
change, and user update requests that include passwords.

SecurityImpact
Change-Id: I3dabb94ab047e86b8730e73416c1a1c333688489
Closes-Bug: #1004114
Closes-Bug: #1327019
Merge "Don't log sensitive auth data"
Merge "Calculate a suitable column width for positional arguments"