Ensure durable is a boolean

Prevent key 'durable' with value 'undefined' being added to the
mc annotations, for example when the durable field was not set, but
another AMQP 1.0 header field was set.

Author: ansd

deps/rabbit/src/mc_amqp.erl

@@ -112,7 +112,7 @@ routing_headers(Msg, Opts) ->
 get_property(durable, Msg) ->
     case Msg of
         #msg{header = #'v1_0.header'{durable = Durable}}
-          when is_atom(Durable) ->
+          when is_boolean(Durable) ->
             Durable;
         #msg{header = #'v1_0.header'{durable = {boolean, Durable}}} ->
             Durable;