[cli-ref] Update python-glanceclient to 2.6.0
[cli-ref] Update python-glanceclient to 2.6.0

Change-Id: Id529ecda41ae19770c07b8c5aeacb4afa292c6cc

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals