tools/qvm-run: handle Ctrl+C nicely
tools/qvm-run: handle Ctrl+C nicely

Do not exit with ugly python backtrace, simply interrupt the command
(propagate SIGINT) and exit.

QubesOS/qubes-issues#4532

marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client,marmarek/qubes-core-mgmt-client