Fix launch.script to not exit prematurely

Use "return" instead of "exit" where possible, especially in
function definitions.

Also fixed the exit codes to match the LSB spec for some specific
conditions (fixes gh-3521).

Fixes gh-3199, fixes gh-3535

spring-boot-samples/spring-boot-sample-devtools/pom.xml

@@ -43,9 +43,6 @@
 			<plugin>
 				<groupId>org.springframework.boot</groupId>
 				<artifactId>spring-boot-maven-plugin</artifactId>
-				<configuration>
-					<executable>false</executable>
-				</configuration>
 			</plugin>
 		</plugins>
 	</build>