Change description for extension
Change description for extension

extension is deprecated in v2.1 so, change wording for it.

Change-Id: I2bc7f494fc0a8057730a8fe28126914dd92a6343
Partial-Bug: #1515222

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