Limit the size of the termination log and allow log input

Enforce the following limits:

12kb for total message length in container status
4kb for the termination message path file
2kb or 80 lines (whichever is shorter) from the log on error

Fallback to log output if the user requests it.

pkg/util/tail/tail_test.go

@@ -0,0 +1,52 @@
+/*
+Copyright 2016 The Kubernetes 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 tail
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestTail(t *testing.T) {
+	line := strings.Repeat("a", blockSize)
+	testBytes := []byte(line + "\n" +
+		line + "\n" +
+		line + "\n" +
+		line + "\n" +
+		line[blockSize/2:]) // incomplete line
+
+	for c, test := range []struct {
+		n     int64
+		start int64
+	}{
+		{n: -1, start: 0},
+		{n: 0, start: int64(len(line)+1) * 4},
+		{n: 1, start: int64(len(line)+1) * 3},
+		{n: 9999, start: 0},
+	} {
+		t.Logf("TestCase #%d: %+v", c, test)
+		r := bytes.NewReader(testBytes)
+		s, err := FindTailLineStartIndex(r, test.n)
+		if err != nil {
+			t.Error(err)
+		}
+		if s != test.start {
+			t.Errorf("%d != %d", s, test.start)
+		}
+	}
+}