clone: add tests for --template and some disallowed option pairs
Some combinations of command-line options to `git clone` are invalid,
but there were previously no tests ensuring those combinations reported
errors. Similarly, `git clone --template` didn't appear to have any
tests.
Helped-by: Jeff King <peff@peff.net> Helped-by: Derrick Stolee <stolee@gmail.com> Signed-off-by: Sean Barag <sean@barag.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>