Run fuzzing tests with go test -fuzz

In addition to oss-fuzz's CIFuzz (see #7052), this commit adds a small
shell script that run all fuzzing tests with go test -fuzz.

While running for 30 seconds would be too short to acutally find issues,
we want to make sure that these fuzzing tests are not fundamentally
broken.

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

script/go-test-fuzz.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+
+#   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.
+
+# Running Go 1.18's fuzzing for 30 seconds each. While this would be too
+# short to acutally find issues, we want to make sure that these fuzzing
+# tests are not fundamentally broken.
+
+set -euo pipefail
+
+fuzztime=30s
+pkgs=$(git grep 'func Fuzz.*testing\.F' | grep -o '.*\/' | sort | uniq)
+
+for pkg in $pkgs
+do
+    go test -fuzz=. ./$pkg -fuzztime=$fuzztime
+done