Unearthed in #361

The TestDenials keeps failing
--- FAIL: TestDenials (159.34s)
mixer_test.go:301: Bad metric value: got 0.000000, want at least 1

@douglas-reid wrote "
when I look at the reported results for this test, I see no 4xx responses when a denial rule is in place. Is this related to the change in error reporting (are we still forwarding rpc statuses to mixer, rather than the internal status messages)? "