clarify need for fencing
clarify need for fencing

Fencing is a crucial requirement, but this is not generally obvious to
those without some HA expertise, so let's clarify the reasons.

Change-Id: I29a82e268c97ff519636a230f4126bac309b6be6
Signed-off-by: Adam Spiers <a3b1ac66d44425905084924ee6cef90b31d2e761@suse.com>

openstack/openstack-user-stories