octavia-operator requires to create OpenStack resources in a custom Tenant of a custom Domain but we still want to use the octavia User from the Default domain.

To support it, gophercloud requires that AuthOptions includes:

• the Username
• the DomainName (of the User)
• the TenantID

https://github.com/gophercloud/gophercloud/blob/849d9ea43b3c0659742ceea3fafb4f0f84b682ec/auth_options.go#L63-L66

lib-common doesn't support setting the TenantID, we have to add the missing field and pass it to gophercloud