FIX: Add line requiring tenant_id to docs

[pratikmallya]

I wasn't able to authenticate without specifying an auth_endpoint and tenant_id. This PR aims at providing that information to future users.

[briancurtin]

Can you share some code to show what you were trying to do? Neither of those settings are needed to authenticate with public cloud.

[briancurtin]

Just getting right to the point: does pyrax.set_setting("identity_type", "rackspace") not work for you?

[pratikmallya]

@briancurtin: i tried again and I don't seem to need the auth_endpoint. But I do need to provide a tenant_id; otherwise the authentication fails

[briancurtin]

You'll have to share some code, failure messages, and your environment then, because that setting has never been needed with public cloud.

[EdLeafe]

If you try to log into the Rackspace public cloud as a user that was created for an account, rather than the main account username, you will need to specify tenant_id.

[sivel]

Looks like based on the discussion, that additional information needs to be added to the documentation stating that the tenant_id is required for RBAC users.