mount.ceph: tweak message on unknown option

The old message sounded worse than it really was,
and was going to stdout instead of stderr.

Fixes: http://tracker.ceph.com/issues/18159
Signed-off-by: John Spray <john.spray@redhat.com>

src/mount/mount.ceph.c

@@ -201,8 +201,10 @@ static char *parse_options(const char *data, int *filesys_flags)
 			skip = 0;
 		} else {
 			skip = 0;
-			if (verboseflag)
-				printf("ceph: Unknown mount option %s\n",data);
+			if (verboseflag) {
+			  fprintf(stderr, "mount.ceph: unrecognized mount option \"%s\", "
+			                  "passing to kernel.\n", data);
+            }
 		}
 
 		/* Copy (possibly modified) option to out */