t/10-basic.t: update for tap_diag redirection

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
t/*: use `dirname` to build source path

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>
tap_ok: exclude tap_* functions from caller info

Signed-off-by: Andrew Gregory <andrew.gregory.8@gmail.com>