OTP 21 compatibility

Author: michaelklishin

src/rabbit_sysmon_handler.erl

@@ -25,6 +25,10 @@
 
 -behaviour(gen_event).
 
+%% Transitional step until we can require Erlang/OTP 21 and
+%% use the now recommended try/catch syntax for obtaining the stack trace.
+-compile(nowarn_deprecated_function).
+
 %% API
 -export([add_handler/0]).