use "crux" for creating users/endpoints

this patch introduces the "crux" [1] tool for creating keystone
users, services, and endpoints in an idempotent fashion.  E.g., to
create a user that doesn't exist:

    $ crux user-create -n lars -t lars -p secret
    creating new tenant
    created tenant lars (d74cec5023c4428da533066bb11943db)
    creating new user lars
    created user lars (adf2c2d92e894a3d90a403c5885f192e)

And performing the same operation a second time:

    $ crux user-create -n lars -t lars -p secret
    using existing tenant lars (d74cec5023c4428da533066bb11943db)
    using existing user lars (adf2c2d92e894a3d90a403c5885f192e)

The behavior is similar for creating keystone endpoints.

[1]: https://github.com/larsks/crux

Change-Id: I694e0c1bdcdde595e1af2ee8ef5d0f239a9ad4cd
Merge "use "crux" for creating users/endpoints"