Increase interactiveness of test* output

Force line buffering for test and test_xi2 to increase interactiveness and
avoid losing data with non-terminal stdout. This fixes capturing xinput
test* output into a file.

Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>