Upgrade to Tomcat 8.5.3

This commit changes the default version of Tomcat to 8.5.3 while
also retaining support for Tomcat 8.0 and 7.0. The main difference
in 8.5 is that the ServerSocketFactory abstraction that allowed the
TrustStore and KeyStore to be configured programatically no longer
exists. This logic has been replaced with the use of a custom URL
protocol (springbootssl) that provides access to the key store and
trust store of an SslStoreProvider. In addition to working with 8.5,
this approach has the advantage of also working with 8.0 and 7.0.

Closes gh-6164

spring-boot-samples/spring-boot-sample-tomcat7-ssl/src/test/java/sample/tomcat/ssl/SampleTomcatSslApplicationTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2016 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.
+ */
+
+package sample.tomcat.ssl;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.boot.context.embedded.LocalServerPort;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
+import org.springframework.boot.test.web.client.TestRestTemplate;
+import org.springframework.boot.test.web.client.TestRestTemplate.HttpClientOption;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
+@DirtiesContext
+public class SampleTomcatSslApplicationTests {
+
+	@LocalServerPort
+	private int port;
+
+	@Test
+	public void testHome() throws Exception {
+		TestRestTemplate testRestTemplate = new TestRestTemplate(HttpClientOption.SSL);
+		ResponseEntity<String> entity = testRestTemplate
+				.getForEntity("https://localhost:" + this.port, String.class);
+		assertThat(entity.getStatusCode()).isEqualTo(HttpStatus.OK);
+		assertThat(entity.getBody()).isEqualTo("Hello, world");
+	}
+
+}