cross-version-config-tests aren't using the right configs

The cross-version-config-tests do not work properly and can't provide any useful feedback.

These tests are supposed to try to start named with configs from system tests from the last released version to ensure we didn't accidentally break backward compatibility. However, the tests are actually executed with new config files and only the previous version of the test framework.

This is caused by overriding the TOP_BUILDDIR variable. The system test files (including configs) are actually copied from the build directory. The reason to copy the test files from the build directory rather than source directory is because some tests also contain compiled files.