Ensure test interpreters are defined before common config

Ensure test interpreters are defined before common config

Nothing from conf.sh.common is required to set these values. On the
contrary, a Python interpreter needs to be set in order to randomize the
algorithm set (which happens in conf.sh.common).

(cherry picked from commit 492992dca8512e6cb2cd44c849656e9fa23b287d)

conf.sh.win32 was modified in addition of the above mentioned commit.