Addons: test_utils.run_distributed fails on GPU

[Squadrick]

The error is:

tensorflow.python.framework.errors_impl.UnknownError: Not enough GPUs to create virtual devices. num_gpus_to_use: 1 #virtual_devices: 2

This happens since number of physical GPUs != number of virtual GPUs.

The line which throws the error is here: gpu_device.cc.

The documentation for tf.config.set_logical_device_configuration seems to run that bit of code successfully.

Relevant log: https://source.cloud.google.com/results/invocations/606014e4-04b9-4cd5-a907-1b7a2661375a/targets/tensorflow_addons%2Fubuntu%2Fgpu%2Fpy3%2Fpresubmit/log

[hyang0129]

@Squadrick I'm willing to take a look at this one. #969 needs to run distributed tests.

[gabrieldemarmiesse]

Closing this as it's going to be tracked in #1682