test-lib: Use "$GIT_BUILD_DIR" instead of "$TEST_DIRECTORY"/../
test-lib: Use "$GIT_BUILD_DIR" instead of "$TEST_DIRECTORY"/../

Change code that used $TEST_DIRECTORY/.. to use $GIT_BUILD_DIR
instead, the two are equivalent, but the latter is easier to read.

This required moving the assignment od GIT_BUILD_DIR to earlier in the
test-lib.sh file.

Signed-off-by: Ævar Arnfjörð Bjarmason <0135fcc047f75af264c800977a73e353c6ba842d@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git