Dockerized integration test

[ldcasillas-progreso]

This patch changes the integration test suite to use the TestContainers library to provision Vault as Docker containers from the official image. This means that apart from setting up Docker, there are no prerequisites for running the integration tests—just running ./gradlew integrationTests will provision and tear down Vault servers for the tests.

All tests pass on my environment (OS X 10.10.4, Docker For Mac 1.12).

Note that this patch is not without its downsides:

1. TestContainers requires Java 8. This is only necessary for running the integration test; I don't know if there is some way to tell Gradle to use Java 7 for everything except the integration test.
2. TestContainers currently doesn't support Docker on Windows.

[steve-perkins]

Thanks so much for the PR, and apologies for it taking so long to get to it.

I absolutely love this idea, but I'd like to hold off for now. A couple of reasons:

• Most of us here at BetterCloud are on OS X or Linux, but there's a broader audience out there. I'm not crazy about taking away the ability to run the integration test suite on Windows machines. I'd like to see if TestContainers (and Docker) work out the cross-platform issues at they matures a bit.
• Again, my own company happens to be on Java 8 across the board, but there are lots of shops that are still on Java 7 (especially for legacy projects). I'm sure we'll drop Java 7 support eventually... but I'd hate to do so simply for the test suite, and I'd like to at least wait for Java 9's release so that we're always maintaining one version back.

[bsideup]

Hey folks,

FYI

1. your product can continue to be on Java 7, only testing environment should be >=8. You can configure Gradle to compile main with 7 and tests with 8
2. TestContainers works on Windows with docker-machine, just not currently tested on a regular basis, see the docs: https://www.testcontainers.org/compatibility.html
3. Docker for Windows support is coming, see Docker for Windows support testcontainers/testcontainers-java#291

We're very welcome new TestContainers users and ready to help and prioritize the issues if they are blockers for you :)

[steve-perkins]

I believe that things have progressed well enough with the TestContainers project that I'm comfortable pulling this in now, and doing away with the current manual integration tests setup.

Unfortunately, this PR has picked up some merge conflicts since it was originally created. I'm not sure if you'd like to merge from master and clean those up here, or resubmit a different PR from a fresh recent branch. But if you're still interested, @ldcasillas-progreso, I'd rather give you a chance to get "credit" for before adding it myself.

[steve-perkins]

It's been about a month, and this looks to be abandoned. Apologies for the length of time that I let it sit in limbo... I just really didn't want to pull the trigger on this until TestContainers support for Windows was in a decent place.

At any rate, since this PR had grown chock full of merge conflicts, I ended up adding TestContainers support in #54 instead.