Make build script executable via python

Add shebang line to make build test suties script callable via command
line without needing python.

Test: ./build/make/ci/build_test_suites --target_product aosp_x86_64
--target_release trunk_staging --with_dexpreopt_boot_img_and_system_server_only --dist_dir <dist_dir> --change_info <change_info_file> <extra_targets>

Change-Id: I94422993e864e021b036a4eb1673b463ad4b86d4