Politely terminating processes with kill hangs the VM backend

[paul-rodriguez]

Using a QEMU backend on a amd64 host, using kill -s TERM or equivalent to kill a running process from the spread shell, a test script inside the VM (or anything else as far as I know) results in the whole VM hanging then displaying this message and exiting:

2023-06-06 11:39:17 Error running debug shell: wait: remote command exited without exit status or exit signal

Note that kill -s KILL still works as expected.