test-lib.sh: Help test_create_repo() find the templates dir

test-lib.sh: Help test_create_repo() find the templates dir

Currently, test_create_repo() expects that templates can be found below
`pwd`/.. This assumption fails when tests are run against a git
installed somewhere else or test_create_repo() is called from
subdirectiories (several tests do this).
Therefore, use $TEST_DIRECTORY as introduced in 2d84e9fb and expect
templates to be present in $TEST_DIRECTORY/.. which should be the root
dir of the git checkout.

Signed-off-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>