server (setup): New setup.py compatible with archlinux PKGBUILD. This file use a new "arch" option in LIBERVIA_INSTALL environment variable (which is set when libervia is installed with PKGBUILD. This setup.py solves the following issues: - os.symlink(os.path.dirname(libervia.__file__), os.path.join(tmp_dir,"libervia")) fails with PKGBUILD because the module libervia is not accessible. - self.custom_create_links() fails with PKGBUILD because the permissions of bin directory is read-only.