Fix a typo in volume API
Fix a typo in volume API

Modification:
  'is read to be attached' => 'is ready to be attached'

Change-Id: I33793e2b0aed97ab35d6775653be24fb2b8a776e
Closes-Bug: #1489748

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