Improvement for glance cache to be automaticly configured

1. Remove glance cache size option from ui and editable cluster attrs.
2. Calculate glance cache size based on formula:
   10%*(/var/lib/glance) if > 5GB else 5GB
3. Tests for new functional
Change-Id: Ibee9b9717fefa5ab7f12b012aa6770317728f890
Merge "Improvement for glance cache to be automaticly configured"