Avoid O_NONBLOCK on stdout in the windows test.

[Random-Liu]

This is a trial to fix the windows test.

See kubernetes/test-infra#14938 for more details.
/cc @BenTheElder

Signed-off-by: Lantao Liu lantaol@google.com

[Random-Liu]

From the log, we can see that O_NONBLOCK is set by mistake:

+ python -c 'import os,sys,fcntl; flags = fcntl.fcntl(sys.stdout, fcntl.F_GETFL); print(flags&os.O_NONBLOCK);'
2048
+ python -c 'import os,sys,fcntl; flags = fcntl.fcntl(sys.stdout, fcntl.F_GETFL); fcntl.fcntl(sys.stdout, fcntl.F_SETFL, flags&~os.O_NONBLOCK);'

So this fix makes sense.

[yujuhong]

/lgtm