test suite: Use http git check for three existing tests

test suite: Use http git check for three existing tests

At the very least we want at least one test which fails when
check_for_git is nobbled ad-hoc [1] to return 1.  "clone-nogit" fits
that bill (verified experimentally).

Pick two other tests to enable this for, roughly arbitrarily.
(Two tests which chain to clone-nogit are affected too.)

Of course we also want a test which fails when check_for_git falsely
returns 0.  We don't have one right now.  Coming up...

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>