Document neutron health monitor and pool properties

This adds descriptions to the properties of OS::Neutron::HealthMonitor
and OS::Neutron::Pool, as well as gettext wrapping for the attributes
description

Closes-Bug: #1224172
Change-Id: I1b7a974b8e8b557bd0ed56f3c08c43f385106738
Merge "Document neutron health monitor and pool properties"