Start couch_log for tests

Now that there's a supervision tree involved we have to start the app to
use it.
diff --git a/src/test_util.erl b/src/test_util.erl
index 88cfc63..3c4d170 100644
--- a/src/test_util.erl
+++ b/src/test_util.erl
@@ -220,7 +220,7 @@
     start(Module, ExtraApps, []).
 
 start(Module, ExtraApps, Options) ->
-    Apps = start_applications([config, ioq, couch_epi | ExtraApps]),
+    Apps = start_applications([config, couch_log, ioq, couch_epi | ExtraApps]),
     ToMock = [config, couch_stats] -- proplists:get_value(dont_mock, Options, []),
     mock(ToMock),
     #test_context{module = Module, mocked = ToMock, started = Apps}.