Add support for tensorflow resource variables (#4438)
Add support for tensorflow resource variables (#4438)

* Adding support for resource variables

Currently resource variable go undetected by the `TensorFlowVariables` since they do not use the same ops for reading values. This change should fix this until a more robust solution is implemented.

* fix varhandle

atumanov/ray,ujvl/ray-ng,ujvl/ray-ng,ray-project/ray,robertnishihara/ray,ray-project/ray,ray-project/ray,richardliaw/ray,pcmoritz/ray-1,pcmoritz/ray-1,pcmoritz/ray-1,ray-project/ray,richardliaw/ray,richardliaw/ray,robertnishihara/ray,ujvl/ray-ng,atumanov/ray,stephanie-wang/ray,stephanie-wang/ray,robertnishihara/ray,robertnishihara/ray,ujvl/ray-ng,pcmoritz/ray-1,stephanie-wang/ray,atumanov/ray,robertnishihara/ray,stephanie-wang/ray,pcmoritz/ray-1,robertnishihara/ray,atumanov/ray,richardliaw/ray,richardliaw/ray,ray-project/ray,atumanov/ray,robertnishihara/ray,stephanie-wang/ray,ray-project/ray,richardliaw/ray,atumanov/ray,richardliaw/ray,pcmoritz/ray-1,atumanov/ray,richardliaw/ray,atumanov/ray,stephanie-wang/ray,robertnishihara/ray,stephanie-wang/ray,stephanie-wang/ray,ray-project/ray,robertnishihara/ray,pcmoritz/ray-1,ray-project/ray,pcmoritz/ray-1,stephanie-wang/ray