got rid of all uses of strerror

This required some minor refactoring of other things and there were some
other small cleanups I noticed along the way.
diff --git a/aos/common/scoped_fd.h b/aos/common/scoped_fd.h
index eb22f80..57ecdd8 100644
--- a/aos/common/scoped_fd.h
+++ b/aos/common/scoped_fd.h
@@ -30,8 +30,7 @@
   void Close() {
     if (fd_ != -1) {
       if (close(fd_) == -1) {
-        LOG(WARNING, "close(%d) failed with %d: %s\n", fd_,
-            errno, strerror(errno));
+        PLOG(WARNING, "close(%d) failed", fd_);
       }
     }
   }