Just a test: Use 2008R2 as base version

[andreasjordan]

Just a test to see which commands would test successfully against the 2008R2 instance.

My plan is to tag those commands to be able to run an extra scenario with 2008R2.

[andreasjordan]

This PR shows that it is possible to test both against 2017/2019 with the latest image and also against 2008R2/2017 with the current image.

It takes a long time to run all the tests, so this should not be used all the time. But we could just comment out the last two scenarios in the matrix-part of the appveyor.yml. Then we can include them from time to time or just run them on the merge to development or just before a new release.

One test against 2019 is currently failing as there is not patch installed in the 2019 instance. We would have to change the test to accept that situation on appveyor.

The two failing tests against 2008 in the last run are due to the instability of some tests - they both succeded in the previous run.

Feedback is welcome.

[niphlod]

again, since I think 2-3 months, "normal" PRs do not run the whole suite, just the tests of the changed functions plus all dependencies. "Long runs" shouldn't be an issue since most PRs target 1 function.