strace: show test suite log on failure

If the tests fail, dump the log so we can see the failures.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 3154a650)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>