Add test for static RepoHooks::onMakeGlobalVariablesScript

This is more like an example how such tests can look.
I know, the test is pretty ugly (mainly because the code it tests
is barely testable) and barely tests anything but having this test
avoids mistakes like in Ieec6829da3a53bfcde3319fd6a6eb4465d2cac4b.

Change-Id: Ib6ab3b8b0d2645cfee9c18662ba297eb61c26edb
Merge "Add test for static RepoHooks::onMakeGlobalVariablesScript"