Clarify health monitor behavior
Clarify health monitor behavior

The basic cookbook document implied that pools without a health
monitor would eventually remove a failed member from the pool.
This will not happen as if there is not health monitor, the members
are assumed as ONLINE.

Change-Id: I6c52f163d8ac0456b4faf7d9bf5cc4a19ee6eeb7

openstack/octavia,openstack/octavia,openstack/octavia