Added Dockerfile for building and running petstore app

Dockerfile

@@ -0,0 +1,13 @@
+FROM maven:3.5-jdk-8 as build
+
+COPY . .
+
+RUN mvn clean package
+
+FROM java:8
+
+COPY --from=build ./juneau-petstore-server/target/juneau-petstore-server-8.1.2-SNAPSHOT.war ./run.war
+
+EXPOSE 5000
+
+ENTRYPOINT ["java","-jar","run.war"]