ptest-runner: Upgrade to 2.4.1

Changes:

cce0edb utils.c: wait_child reimplement timeout using alarm
acbba90 utils.c: Use a thread to read from child
cb2840a utils.c: Fix exit status of a child
77bc79e utils.c: get_available_ptests allow to specify relative directories
d27e242 README.md: Small fix mtrace call
c5d5831 tests/utils.c: Add braces in START_TEST/END_TEST now required in check 0.15.x

Signed-off-by: Aníbal Limón <anibal.limon@linaro.org>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>