Multiple GPUs not supported with Tensorflow Backend

[ashao]

Description

Trying to use the multi-gpu functions with Tensorflow models raises an error within RedisAI. This likely seems to be an incompatibility with the call to the Tensorflow backend. Note that we can confirm that multi-gpu works for Torch models.

How to reproduce

1. Create a Tensorflow model
2. Use the set_model_multigpu to load this into the database.
3. Error gets raised in the database

Expected behavior

Users should be able to set Tensorflow models and deploy on multi-gpu machines