Change default directories of system tests. Use configure directories
I started playing with out-of-tree builds recently. But I could not find an easy way to start tests in bin/tests/system with build made in external directory. This change will make much more simple to run tests against extra build. After external build is complete, just make symlink into source bin/tests/system conf.sh from the build directory. Then tests can be started from source directory without additional changes.
This is especially useful when testing different build configuration from the same sources.