tests: sync tests/utils/tap with Babeltrace repository

tests: sync tests/utils/tap with Babeltrace repository

There are a few fixes / improvements in the Babeltrace version of the
tap library, bring them here.  The Babeltrace commit used is
0022a87819b0 ("Fix: clear_string_field(): set first character to 0") In
particular, I'm looking for the TAP_PRINTF_FORMAT fixes, to be able to
enable -Wsuggest-attribute=format.  But I think it's easier to keep them
in sync, so bring in all changes, instead of just the TAP_PRINTF_FORMAT
ones.

The only diff not brought are the semicolons in the pass / fail
definitions, which were removed in the previous patch.  Those changes
should be brought to the Babeltrace repository.

Bringing in the TAP_PRINTF_FORMAT changes finds a few format string
mistakes in the tests, fix them.

Change-Id: I0d125b313265e72303be8d704ba40554bca87cd1
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>