The "/tokens" path is explicitly appended to the OS_AUTH_URL
by the configure_tempest.sh tool, but this is also appended
internally by glance:
https://github.com/openstack/glance/blob/master/glance/common/auth.py#L111
leading to a duplicated "/tokens/tokens" path.
Change-Id: I2ea49289f7e1976346eff220dc3d1664bdad4fb0