change CHECK to LOG(ERROR) when pipe read error on NotificationQueue

Summary: The check was originally added to track down cpu pinning issue. In reality the check did get triggered, so change to soft error to calm the crazy nag bot. what's wrong with you.
We need to see the soft error log to find out what the error is.

Reviewed By: mzlee

Differential Revision: D2632752

fb-gh-sync-id: 87c11b186f97f0eb4a6c5ac13a1117b280198673

folly/io/async/NotificationQueue.h

@@ -511,7 +511,9 @@ class NotificationQueue {
     if (rc < 0) {
       // EAGAIN should pretty much be the only error we can ever get.
       // This means someone else already processed the only available message.
-      CHECK_EQ(errno, EAGAIN);
+      if (rc != EAGAIN) {
+        LOG(ERROR) << "non-EAGAIN error returned on pipe read: " << errno;
+      }
       return false;
     }
     assert(value == 1);