bitbake: hashserv: improve the loglevel error message to be more helpful

Coming from a kernel background, I was thinking along the lines of

	dmesg -n <integer>

for loglevel adjustments.  So I tried various large and small and
even zero number values with no luck before getting frustrated and
opening up the python.

Let us save others the frustration and give a hint what the args it
expects should look like.

(Bitbake rev: df184b2a4e80fca847cfe90644110b74a1af613e)

Signed-off-by: Paul Gortmaker <paulg@kernel.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake-hashserv

@@ -132,7 +132,7 @@ The following permissions are supported by the server:
 
     level = getattr(logging, args.log.upper(), None)
     if not isinstance(level, int):
-        raise ValueError("Invalid log level: %s" % args.log)
+        raise ValueError("Invalid log level: %s (Try ERROR/WARNING/INFO/DEBUG)" % args.log)
 
     logger.setLevel(level)
     console = logging.StreamHandler()