Alternative means of detecting SUT termination for Scandium/JSSE

[pfg666]

The test programs for Scandium/JSSE are not the SUT themselves, but instead act as 'SUT launchers'. Hence, detecting when the SUT process terminates cannot be based the termination of the process running the test program (the test launcher stays active during the learning run). Instead, detection for these implementations relies on network errors signaled via ICMP packets.

Unfortunately, in later versions of TLS-Attacker network errors due to ICMP packets are no longer visible (see relevant issue). Hence, we need a different mechanism of detecting when the SUT is down.