Add note about protected properties in glance

Also add glossary term

Closes-Bug: #1219863

Change-Id: Id30dcbd635d933c206b2a314344dce3d5102dec0
author: diane fleming
Add "protected property" term to glossary

Closes-Bug: #1219863

Change-Id: I01fbdcae1e98edda463c397c455cf959368d1548
author: diane fleming
Merge "Add note about protected properties in glance"