Add ?awaitMatch macro

awaitMatch(Guard, Expr, Timeout) reevaluates Expr until it matches
Guard up to Timeout milliseconds from now. It returns the matched
value, in the event said value is useful later in a test.

Additionally simplify an instance of ?assertEqual(true, ... to ?assert(

deps/rabbitmq_ct_helpers/include/rabbit_assert.hrl

@@ -0,0 +1,21 @@
+-define(awaitMatch(Guard, Expr, Timeout),
+        begin
+            ((fun Filter(Horizon) ->
+                      R = Expr,
+                      case (R) of
+                          Guard -> R;
+                          __V -> case erlang:system_time(millisecond) of
+                                     Now when Now < Horizon ->
+                                         timer:sleep(min(50, Horizon - Now)),
+                                         Filter(Horizon);
+                                     _ ->
+                                         erlang:error({awaitMatch,
+                                                       [{module, ?MODULE},
+                                                        {line, ?LINE},
+                                                        {expression, (??Expr)},
+                                                        {pattern, (??Guard)},
+                                                        {value, __V}]})
+                                 end
+                      end
+              end)(erlang:system_time(millisecond) + Timeout))
+        end).

deps/rabbitmq_ct_helpers/src/rabbit_ct_proper_helpers.erl

@@ -20,8 +20,7 @@
 -export([run_proper/3]).
 
 run_proper(Fun, Args, NumTests) ->
-    ?assertEqual(
-       true,
+    ?assert(
        proper:counterexample(erlang:apply(Fun, Args),
 			     [{numtests, NumTests},
 			      {on_output, fun(".", _) -> ok; % don't print the '.'s on new lines