functional test refactoring: resign form option to preload libraries

Instead of passing preloaded libraries to setup_dp.sh script, now
functional tests may change configuration in fixtures scripts.
Script setup_db.sh is not affected by configuration changes required
by the tests. The main reason of the change is to avoid overriding
original server configuration by the tests, i.e if a postgres was
configured with its own preloade libraries, then previously test
override this settings and original preloaded libraries were lost.