mavsdk_tests: properly exit on Ctrl+C
mavsdk_tests: properly exit on Ctrl+C

With threads we need to manually take care of it, otherwise it gets
messy and we need to press Ctrl+C multiple times.

krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,PX4/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,PX4/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,acfloria/Firmware,acfloria/Firmware