Clarify checksum_base_images glance flag doc

fixes bug 1075021

changes were made to grizzly that make this behaviour more clear/
correct.

Change-Id: I8099d86788312d387f13678610041e8a07cc4230
Rebuild the architecture of HA Doc

Change-Id: If3deb493fd1cb0a624601bad6f2196f47ac4e8fb