Ensure startup failures are only logged once

Update SpringApplication so that startup exceptions are only logged
once. A custom UncaughtExceptionHandler is now used when running in
the main thread to suppress errors that have already been logged.

Fixes gh-4423

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/autoconfigure/FileWatchingFailureHandler.java

@@ -42,7 +42,6 @@ class FileWatchingFailureHandler implements FailureHandler {
 
 	@Override
 	public Outcome handle(Throwable failure) {
-		failure.printStackTrace();
 		CountDownLatch latch = new CountDownLatch(1);
 		FileSystemWatcher watcher = this.fileSystemWatcherFactory.getFileSystemWatcher();
 		watcher.addSourceFolders(

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/RestartLauncher.java

@@ -50,6 +50,7 @@ class RestartLauncher extends Thread {
 		}
 		catch (Throwable ex) {
 			this.error = ex;
+			getUncaughtExceptionHandler().uncaughtException(this, ex);
 		}
 	}
 

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/Restarter.java

@@ -271,10 +271,7 @@ public class Restarter {
 				return;
 			}
 			if (failureHandler.handle(error) == Outcome.ABORT) {
-				if (error instanceof Exception) {
-					throw (Exception) error;
-				}
-				throw new Exception(error);
+				return;
 			}
 		}
 		while (true);