test-bzr.sh, test-hg.sh: allow running from any dir

test-bzr.sh, test-hg.sh: allow running from any dir

Set TEST_DIRECTORY to the t/ directory (if TEST_DIRECTORY is not
already set) so that the user doesn't already have to be in the test
directory to run these test scripts.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Based-on-patch-by: Richard Hansen <rhansen@bbn.com>
Reviewed-by: Richard Hansen <rhansen@bbn.com>
Signed-off-by: Richard Hansen <rhansen@bbn.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>