Add test to check basho/riak_kv#1022 - client/bprop delete mode.

Needs to be separately merged to 2.0.
If you want to do the waiting in a more r_t idiomatic way you could make these changes:

```
diff --git a/tests/verify_riak_client_delete_mode.erl b/tests/verify_riak_client_delete_mode.erl
index 351df80..64196bc 100644
--- a/tests/verify_riak_client_delete_mode.erl
+++ b/tests/verify_riak_client_delete_mode.erl
@@ -82,7 +82,8 @@ confirm() ->
     %% assume mechanism works).
     ?assertEqual(<<>>, verify_delete(Node1, <<"fromclient">>, <<"after500">>, 500)),
     timer:sleep(500), % wait for the delete time to expire, then check
-    ?assert(object_really_removed(Node1, <<"fromclient">>, <<"after500">>, 5000)),
+    rt:wait_until(object_really_removed(Node1, <<"fromclient">>, <<"after500">>)),
+    ?assertEqual({error, notfound}, verify_delete(Node1, <<"fromclient">>, <<"after500">>, 500)),
     lager:info("...checked delayed"),
 
     %%
@@ -111,7 +112,8 @@ confirm() ->
     %% assume mechanism works).
     ?assertEqual(<<>>, verify_delete(Node1, <<"afterbucket">>, <<"after500">>, 500)),
     timer:sleep(500), % wait for the delete time, then start looking
-    ?assert(object_really_removed(Node1, <<"afterbucket">>, <<"after500">>, 5000)),
+    rt:wait_until(object_really_removed(Node1, <<"afterbucket">>, <<"after500">>)),
+    ?assertEqual({error, notfound}, verify_delete(Node1, <<"afterbucket">>, <<"after500">>, 500)),
     lager:info("...checked delayed"),
 
 
@@ -125,22 +127,21 @@ confirm() ->
 %%
 %% -------------------------------------------------------------------
 
-object_really_removed(_Node, _Bucket, _Key, Remaining) when Remaining < 0 ->
-    false;
-object_really_removed(Node, Bucket, Key, Remaining) ->
-    case vnode_get_value(Node, Bucket, Key) of
-        {error, notfound} ->
-            true;
-        _ ->
-            timer:sleep(100),
-            object_really_removed(Node, Bucket, Key, Remaining - 100)
+object_really_removed(Node, Bucket, Key) ->
+    fun() ->
+            case vnode_get_value(Node, Bucket, Key) of
+                {error, notfound} ->
+                    true;
+                _ ->
+                    false
+            end
     end.
```