Add general utility to deal with lambda callbacks

Add `LambdaSafe` utility that provides a consistent way to deal with
the problems that can occur when calling lambda based callbacks.

See gh-11584

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/util/package-info.java

+/*
+ * Copyright 2012-2018 the original author or 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.
+ */
+
+/**
+ * Contains miscellaneous utility classes.
+ */
+package org.springframework.boot.util;