[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>

python/ray/serve/examples/doc/tutorial_sklearn.py

@@ -1,4 +1,5 @@
 # yapf: disable
+import ray
 # __doc_import_begin__
 from ray import serve
 
@@ -70,6 +71,7 @@ class BoostingModel:
 
 # __doc_define_servable_end__
 
+ray.init(num_cpus=8)
 # __doc_deploy_begin__
 client = serve.start()
 client.create_backend("lr:v1", BoostingModel)