Glance's Keystone endpoint does not need the '/v1'

As said in [1], “This is useless and causes problem with library using
glanceclient. Glance has already a workaround for this […]”

[1] https://review.openstack.org/#/c/18325/
And don't forget to update the tests !
Merge pull request #66 from fcharlier/fc/fix_endpoint

Glance's Keystone endpoint does not need the '/v1'