Add a separate provisioning script to install Xcode if it's not already installed on the bot.
For some unknown reason it needs to be a separate script, otherwise the provisionator will complain it doesn't know the required GitHub token to download Xcode.
Fixes https://github.com/xamarin/xamarin-macios/issues/6326.
Mono know provides a set of testing assemblies that contain the tests to be ran in each of the supported platforms. This commit adds the following:
1. Two different runners that can be used to execute NUnit and xUnit tests.
2. The necessary glue to get xharness to run the new tests and report the results.
3. A new test that will ensure that if mono adds new tests, xharness will report failures if the tests are not run or not ignored.
Those tests needs to be run with the linker disabled since they use
reflection for most of their work.
The original dontlink (for linker tests) was becoming too large in
some configuration (e.g. tvOS release with bitcode) but this was
due to other BCL assemblies (not the introspection tests)
Rolf Bjarne Kvinge
Manuel de la Pena
monojenkins
Vincent Dondain
Marek Safar
Sebastien Pouliot