Corrects a typo in RESTful Web API (v1) document

The typo /v1/nodes/<uuid>/state is changed to /v1/nodes/<uuid>/states
Closes-Bug: 1311285

Change-Id: I66bc695298c04b423c9c9be45b23fce5b60727f0
Merge "Corrects a typo in RESTful Web API (v1) document"