Create a dummy session in tf_cnn_benchmarks to properly initialize globals
Create a dummy session in tf_cnn_benchmarks to properly initialize globals

Nasnet model uses is_gpu_available function that also initializes GPUDevices
using default ConfigProto. This will then cause it to silently ignore some of the
fields passed while constructing new sessions. Creating a dummy session in the
beginning will work around the issue by creating GPUDevices with the right
configurations.

PiperOrigin-RevId: 215231430

annarev/benchmarks,tensorflow/benchmarks,annarev/benchmarks,tensorflow/benchmarks