tests: Stop test run on NOTE command failure

tests: Stop test run on NOTE command failure

There is no point trying to go through a test case if the NOTE command
to write TEST-START entry does not succeed. This avoids some excessive
waits on buildbot trying to forcefully kill the programs on its timeout
if wpa_supplicant gets stuck waiting for something (like the current
issue with libnl events and commands having a chance of hitting a
blocking wait on netlink messages).

Signed-hostap: Jouni Malinen <j@w1.fi>