buggood first issuetests
Description
We YOLO-pull st2tests master in st2-self-check script. This makes script broken on older st2 versions.
So st2-self-check should rely on versioned branches in st2tests.
TODO: Parse https://github.com/StackStorm/st2/blob/master/st2common/st2common/__init__.py to determine the correct git vX.Y branch to get.