RegressionTestSuite - support multiple repos

[kmanning]

• On Vipar, our IsolatedTestSuites require both the automation test suite, and the application code base (ie: 2 SCM's). RegressionTestSuite doesn't currently support this.
• Allow support for multiple SCMs
• Allow support for cding into a specific directory before executing the test suite.
• Example code:

def testQa = new RegressionStage().withScm(git@SomeHost:SomeTeam/SomeAutomationRepository.git')
                                  .withScm(git@SomeHost:SomeTeam/ApplicationRepo.git')
                                  .changeDirectory('applicationRepo')
...
validate.then(deployQa)
        .then(testQa)

1. If withScm is called once, then it will use only that repo
2. If withScm is called multiple times, it becomes cumulative. All scm's are checked out, and they'll all be checked out into a subdirectory that matches their project name. If withScm was only called once, it DOES NOT get checked out into a subdirectory. (For later, if withScm is not called at all, then the same repo that contains the Jenkinsfile is used, and it too, is NOT checked out into a subdirectory).
3. If changeDirectory is called, then cd <subdirectory> is added to the ./bin/test.sh command. (ie: if you're using multiple repos, cd into a specific repo to find the ./bin/test.sh command).