Generalize DropwizardAppRule for other test frameworks

Hi,

I was looking at starting/stopping a Dropwizard app in Cucumber tests and DropwizardAppRule has all the functionality I need but obviously it doesn't expose startIfRequired and stop methods.

I'd happy to extract a DropWizardAppTestSupport class from DropwizardAppRule and make the DropwizardAppRule depend on that and contribute the code if there's any interest.

What do you think?

Thanks,
Csaba