Build error and runtime errors with Java pack fixed

1)
The artifact name built was helloworld.jar but the copy command was referring to different name hence build is failing:
```
Step 6/8 : COPY --from=BUILD /usr/src/app/target/app.jar /opt/app.jar
lstat usr/src/app/target/app.jar: no such file or directory
```
Fixed by copying helloworld.jar instead of app.jar

2) Since the jar being deployed was a thin jar without dependencies, it was not able to find Spark classes and thus failing:

```
2017-07-03T10:23:49.370518638Z Exception in thread "main" java.lang.BootstrapMethodError: java.lang.NoClassDefFoundError: spark/Request
2017-07-03T10:23:49.373134679Z 	at helloworld.Hello.main(Hello.java:7)
2017-07-03T10:23:49.373163432Z Caused by: java.lang.NoClassDefFoundError: spark/Request
2017-07-03T10:23:49.373167578Z 	... 1 more
2017-07-03T10:23:49.373170484Z Caused by: java.lang.ClassNotFoundException: spark.Request
2017-07-03T10:23:49.373173097Z 	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
2017-07-03T10:23:49.373175661Z 	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
2017-07-03T10:23:49.373178321Z 	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335)
2017-07-03T10:23:49.373180932Z 	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
2017-07-03T10:23:49.373183512Z 	... 1 more
```
Fixed by using the "-with-dependency" jar

packs/maven/Dockerfile

@@ -5,6 +5,6 @@ RUN mvn -f /usr/src/app/pom.xml clean package
 
 FROM openjdk:8-jdk-alpine
 EXPOSE 4567
-COPY --from=BUILD /usr/src/app/target/app.jar /opt/app.jar
+COPY --from=BUILD /usr/src/app/target/helloworld-jar-with-dependencies.jar /opt/app.jar
 WORKDIR /opt
 CMD ["java", "-jar", "app.jar"]