tests: handle NO_PYTHON setting

tests: handle NO_PYTHON setting

Without this, test-lib checks that the git_remote_helpers
directory has been built. However, if we are building
without python, we will not have done anything at all in
that directory, and test-lib's sanity check will fail.

We bump the inclusion of GIT-BUILD-OPTIONS further up in
test-lib; it contains configuration, and as such should be
read before we do any checks (and in this particular case,
we need its value to do our check properly).

Signed-off-by: Jeff King <peff@peff.net>
Looks-fine-to-me-by: Brandon Casey <brandon.casey.ctr@nrlssc.navy.mil>
Acked-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>