Add configuration of repo to VertxJUnit4ClassRunner

[johnoliver]

Since the recent domain change of github to github.io for the module repository, this has broken almost all of our tests, and currently vertx-junit-annotations does not offer any way to configure the repository. This is a very major issue for us as we are using it in a commercial environment and is causing us to ignore tests in order to prevent it from blocking our release.

Unfortunately since HEAD appears to have moved on since to support vertx 2 adding this to the current HEAD will not be of any use to us for a while. I have made a branch that applies the fix to the last release. Is it possible to get this released from a branch as a back ported fix to support vertx 1.x? I believe going forward it would also be a reasonable configuration option to have even in the vertx 2 version.

The branch is at:

https://github.com/johnoliver/vertx-junit-annotations/tree/repo-fix-backport

and the specific patch is:

johnoliver@c0e8d00