Do not query GPU compatibility before app main (#6679)
Do not query GPU compatibility before app main (#6679)

tf.test.is_gpu_available() should not be called in flags since this is
called before app.main() and the runtime has not yet been initialized.
tombstone/models,tombstone/models,tombstone/models,alexgorban/models,tombstone/models,tombstone/models,derekjchow/models,alexgorban/models,derekjchow/models,alexgorban/models,derekjchow/models,tombstone/models,derekjchow/models,derekjchow/models,alexgorban/models,alexgorban/models