Add integration tests for default launch script

This commit adds a suit of integration tests for the launch script. See
the accompanying README.adoc for further details.

Closes gh-4872

spring-boot-integration-tests/spring-boot-launch-script-tests/README.adoc

@@ -0,0 +1,75 @@
+= Spring Boot Launch Script Tests
+
+This module contains integration tests for the default launch script that is used
+to make a jar file fully executable on Linux. The tests use Docker to verify the
+functionality in a variety of Linux distributions.
+
+== Setting up Docker
+
+The setup that's required varies depending on your operating system.
+
+=== Docker on OS X
+
+Docker relies on Linux kernel features so the Docker Daemon must be run inside a Linux VM.
+Following the https://docs.docker.com/engine/installation/mac/[OS X installation
+instructions] to install Docker Toolbox which uses VirtualBox to host the required VM.
+
+=== Docker on Linux
+
+Install Docker as appropriate for your Linux distribution. See the
+https://docs.docker.com/engine/installation/[Linux installation instructions] for more
+information.
+
+Next, add your user to the `docker` group. For example:
+
+----
+$ sudo usermod -a -G docker awilkinson
+----
+
+You may need to log out and back in again for this change to take affect and for your
+user to be able to connect to the daemon.
+
+== Preparing to run the tests
+
+Before running the tests, you must prepare your environment according to your operating
+system.
+
+=== Preparation on OS X
+
+The tests must be run in an environment where various environment variables including
+`DOCKER_HOST` and `DOCKER_CERT_PATH` have been set:
+
+----
+$ eval $(docker-machine env default)
+----
+
+=== Preparation on Linux
+
+Docker Daemon's default configuration on Linux uses a Unix socket for communication.
+However, Docker's Java client uses HTTP by default. Docker Java's client can be configured
+to use the Unix socket via the `DOCKER_URL` environment variable:
+
+----
+$ export DOCKER_URL=unix:///var/run/docker.sock
+----
+
+== Running the tests
+
+You're now ready to run the tests. Assuming that you're in the same directory as this
+README, the tests can be launched as follows:
+
+----
+$ mvn -Pdocker clean verify
+----
+
+The first time the tests are run, Docker will create the container images that are used to
+run the tests. This can take several minutes, particularly if you have a slow network
+connection. Subsequent runs will be faster as the images are cached locally. You can run
+`docker images` to see a list of the cached images.
+
+== Cleaning up
+
+If you want to reclaim the disk space used by the cached images (at the expense of having
+to wait for them to be downloaded and rebuilt the next time you run the tests), you can
+use `docker images` to list the images and `docker rmi <image>` to delete them. See
+`docker rmi --help` for further details.