Revised wording regarding HA capabilites

Text originally stated that HA prevents node failures, which may result
in a mismatch with user expectations. Revised statement to clarify that
HA helps mitigate the impact of individual node failures.

Change-Id: I805a642ee6020ca53c27c120a811ca7349a2f14f
Partial-Bug: #1217503
Merge "Revised wording regarding HA capabilites"