launch.groovy never updates existing projects

https://github.com/checkstyle/contribution/blob/f3d29c6ed10b697c9a7e513651e15133cc513d85/checkstyle-tester/launch.groovy#L106-L113

When we run the program once, we clone the repositories and get the latest data.
When we run the program future times, we never do a fetch. Long time users who constantly use this tool will never be running on the latest projects and they will never update these repositories by hand.

I feel we should force users to use the latest code for the project if a specific commit is not specified.
We might want to consider doing resets/cleans in case we change from a specific commit to no commit, or if the user plays around with the repository for some reason, to verify the project is in the state we wish to test.

It was mentioned part of the reason this was not done was so the tool could be used in an offline mode and doing a fetch will break this. We can get around this by either 1) ignoring a failed fetch or 2) adding a new option `-dontFetchUpdates` (or some other name).