tests: Stop valgrind.bin regardless of which option is started

tests: Stop valgrind.bin regardless of which option is started

The previous design of having to provide valgrind parameter to
stop-wifi.sh did not work since the new test setup may no match the
previous one. Instead of trying to figure out what needs to be stopped
based on previous run, stop all wpa_supplicant/hostapd processes running
under valgrind unconditionally to avoid cases where new set of processes
cannot be started due to existing processed.

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