Tests: Move TAP helpers to tests/utils/tap

Tests: Move TAP helpers to tests/utils/tap

tests/utils/tap/tap.{h,c}:
For use in C tests. You can link against libtap with the usual automake
mechanisms.

New TAP helper:

tests/utils/tap/tap.sh:
For use in shell scripts tests. Source the script
(e.g. source "tests/utils/tap/tap.sh") to use the relevants TAP
functions.

Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>