Executor class leaves processes running after cancellation

[FrankD412]

When testing PR 345, the sample specification for LULESH using the LocalPoolAdapter leaves long-running processes when a cancellation is requested. It seems that the Executor class does not use the proper process kill to remove these processes.

[FrankD412]

After some time debugging, it looks as though the method Executor._Record.cancel was only terminating then killing the children. The missing call to terminate the parent made the assumption that the children would terminate and then be killed, but never touches the parent. That means the hard "eviction" of the process never happens.

[FrankD412]

Accidentally pushed to main.. Fixed by commit ac6cee92112ffa659ccf1016a71451022cb0b23c