Make OpenSSL::Test::setup() a bit more forgiving

It was unexpected that OpenSSL::Test::setup() should be called twice
by the same recipe.  However, that may happen if a recipe combines
OpenSSL::Test and OpenSSL::Test::Simple, which can be a sensible thing
to do.  Therefore, we now allow it.

Reviewed-by: Rich Salz <rsalz@openssl.org>