Samples cleanup

- Modifying dependencies to starter-web with tomcat exclusion plus
  alternative servlet container instead of manual dependency on
  spring-webmvc as it is the preferrable way to use alternative servlet
  container
- Previously RestTemplate with ssl was configured manually in tests - now
  it rellies on autoconfiguration - changed this for multi-connector test
  and added test to ensure that ssl autoconfiguration is working
- Most samples with alterntative servlet containers used some kind of
  service reading property and returning default since it wasn't
  configured - removed it, since it is not specific to using alternative
  servlet containers.

See gh-10548

spring-boot-samples/spring-boot-sample-websocket-jetty/src/test/java/samples/websocket/jetty/SampleWebSocketsApplicationTests.java

@@ -38,7 +38,6 @@ import org.springframework.boot.web.server.LocalServerPort;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.web.socket.client.WebSocketConnectionManager;
 import org.springframework.web.socket.client.standard.StandardWebSocketClient;
@@ -47,7 +46,6 @@ import static org.assertj.core.api.Assertions.assertThat;
 
 @RunWith(SpringRunner.class)
 @SpringBootTest(classes = SampleJettyWebSocketsApplication.class, webEnvironment = WebEnvironment.RANDOM_PORT)
-@DirtiesContext
 public class SampleWebSocketsApplicationTests {
 
 	private static Log logger = LogFactory.getLog(SampleWebSocketsApplicationTests.class);

spring-boot-samples/spring-boot-sample-websocket-jetty/src/test/java/samples/websocket/jetty/echo/CustomContainerWebSocketsApplicationTests.java

@@ -42,7 +42,6 @@ import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
 import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
-import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.junit4.SpringRunner;
 import org.springframework.web.socket.client.WebSocketConnectionManager;
 import org.springframework.web.socket.client.standard.StandardWebSocketClient;
@@ -52,7 +51,6 @@ import static org.assertj.core.api.Assertions.assertThat;
 @RunWith(SpringRunner.class)
 @SpringBootTest(classes = { SampleJettyWebSocketsApplication.class,
 		CustomContainerConfiguration.class }, webEnvironment = WebEnvironment.RANDOM_PORT)
-@DirtiesContext
 public class CustomContainerWebSocketsApplicationTests {
 
 	private static Log logger = LogFactory