Did the rename of the VR namespace to XR not make the merge into the 2017 release build?
It should be in all public builds of 2017.2. Where are you not seeing it as UnityEngine.XR?
2017.1 live release. My bad. Got my versions mixed up.
I had a project I was tinkering with in b2, and thought I should move it to the supported version which just got released, not picking up that the beta stream had moved ahead.