Add testing log hook to context

Allows log output to sent along with test output
for cleaner output and clearer ordering.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

log/logtest/log_hook.go

@@ -0,0 +1,42 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package logtest
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/sirupsen/logrus"
+)
+
+type testHook struct {
+	t   testing.TB
+	fmt logrus.Formatter
+}
+
+func (*testHook) Levels() []logrus.Level {
+	return logrus.AllLevels
+}
+
+func (h *testHook) Fire(e *logrus.Entry) error {
+	s, err := h.fmt.Format(e)
+	if err != nil {
+		return err
+	}
+	h.t.Log(string(bytes.TrimRight(s, "\n")))
+	return nil
+}