Add description for os-hosts
Add description for os-hosts

some virt driver code don't support all host functions

Change-Id: Ia6d448706ca33809f155d8ab66df3ce737f51f0f
Partial-Bug: #1515222

Tesora/tesora-api-site,openstack/api-site,Tesora/tesora-api-site,openstack/api-site,openstack/api-site,Tesora/tesora-api-site,Tesora/tesora-api-site,openstack/api-site,Tesora/tesora-api-site,Tesora/tesora-api-site,Tesora/tesora-api-site