Log this to stderr

Per suggestion from @lukebakken.

References #1307.
[Finishes #149635897]

Author: michaelklishin

src/rabbit.erl

@@ -811,7 +811,7 @@ start(normal, []) ->
             Args = [OTPRel, ERTSVer, ?OTP_MINIMUM, ?ERTS_MINIMUM],
             rabbit_log:error(Msg, Args),
             %% also print to stdout to make this more visible
-            io:format("Error: " ++ Msg ++ "~n", Args),
+            io:format(standard_error, "Error: " ++ Msg ++ "~n", Args),
             {error, {erlang_version_too_old, rabbit_misc:format("Erlang ~s or later is required, started on ~s", [?OTP_MINIMUM, OTPRel])}};
         Error ->
             Error