[docker] Detect CPUs in container correctly (#10507)

Co-authored-by: simon-mo <simon.mo@hey.com>
Co-authored-by: Richard Liaw <rliaw@berkeley.edu>
Co-authored-by: Alex Wu <itswu.alex@gmail.com>

doc/source/tune/_tutorials/tune-serve-integration-mnist.py

@@ -97,6 +97,7 @@ import torch
 import torch.nn as nn
 import torch.nn.functional as F
 import torch.optim as optim
+import ray
 from ray import tune, serve
 from ray.serve.exceptions import RayServeException
 from ray.tune import CLIReporter
@@ -613,6 +614,9 @@ if __name__ == "__main__":
 
     args = parser.parse_args()
 
+    if args.smoke_test:
+        ray.init(num_cpus=2)
+
     model_dir = os.path.expanduser(args.model_dir)
 
     if args.query >= 0: