[caffe2][tpx] log to stderr (pytorch#42162)

Summary: Pull Request resolved: pytorch#42162

Test Plan: CI

Reviewed By: mrshenli

Differential Revision: D22791440

fbshipit-source-id: 14f16cd7a94a57161c5724177b518527f486232d

Author: Sandeep Kumar Pani

test/distributed/test_nccl.py

@@ -18,7 +18,8 @@
 
 nGPUs = torch.cuda.device_count()
 if not TEST_CUDA:
-    print('CUDA not available, skipping tests')
+    import sys
+    print('CUDA not available, skipping tests', file=sys.stderr)
     TestCase = object  # noqa: F811