Clear logback status list on reset

Update LogbackLoggingSystem to clear logback status messages on reset.
This prevents shutdown errors from preventing subsequent startup.

Fixes gh-3472

spring-boot-samples/spring-boot-sample-tomcat-jsp/.gitignore

@@ -0,0 +1 @@
+/target/

spring-boot-samples/spring-boot-sample-tomcat7-jsp/.gitignore

@@ -0,0 +1 @@
+/target/

spring-boot-samples/spring-boot-sample-traditional/.gitignore

@@ -0,0 +1 @@
+/target/

spring-boot-samples/spring-boot-sample-web-jsp/.gitignore

@@ -0,0 +1 @@
+/target/

spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java

@@ -168,6 +168,7 @@ public class LogbackLoggingSystem extends Slf4JLoggingSystem {
 	@Override
 	protected void reinitialize(LoggingInitializationContext initializationContext) {
 		getLoggerContext().reset();
+		getLoggerContext().getStatusManager().clear();
 		loadConfiguration(initializationContext, getSelfInitializationConfig(), null);
 	}