we still invoke ssh unnecessarily when there in incompatible or erreneous input
The fallow-up to finish that would make the code a bit more verbose,
as it would require repeating this bit:
```
r = bus_connect_transport(arg_transport, arg_host, false, &bus);
if (r < 0) {
log_error_errno(r, "Failed to create bus connection: %m");
goto finish;
}
sd_bus_set_allow_interactive_authorization(bus, arg_ask_password);
```
in every verb, after parsing.
v2: add waitpid() to avoid a zombie process, switch to SIGTERM from SIGKILL
v3: refactor, wait in bus_start_address()
392cf1d05d