Clean up a confusing gclient_utils.py message

While setting up a Chromium repo on a new machine I ended up with a
missing .gclient_entries file. This triggered a warning message but it
led me in the wrong direction. I think that the new message - saying
exactly what problem was detected - will be slightly more helpful.

Change-Id: I8c91861f843e3d30881b1b4933a02ad966c114ef
Reviewed-on: https://chromium-review.googlesource.com/533314Reviewed-by: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

gclient_utils.py

@@ -613,8 +613,9 @@ def FindGclientRoot(from_dir, filename='.gclient'):
       # might have failed. In that case, we cannot verify that the .gclient
       # is the one we want to use. In order to not to cause too much trouble,
       # just issue a warning and return the path anyway.
-      print >> sys.stderr, ("%s file in parent directory %s might not be the "
-          "file you want to use" % (filename, path))
+      print >> sys.stderr, ("%s missing, %s file in parent directory %s might "
+          "not be the file you want to use." %
+          (entries_filename, filename, path))
       return path
     scope = {}
     try: