utils: Improve WaitLocalProcess

Previously, the hypervisors were sending a signal and then checking to
see if the process had died by sending the magic null signal (`0`). However,
that doesn't work as it was written: the logic was assuming sending the
null signal to a process that was dead would return `ESRCH`, but it
doesn't: you first need to you `wait(2)` for the process before sending
that signal. This means that previously, all affected hypervisors would
appear to take `timeout` seconds to end, even though they had _already_
finished.

Now, the hypervisors true end time will be seen as we wait for the
processes before sending the null signal to ensure the process has
finished.

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

src/runtime/virtcontainers/utils/utils.go

@@ -349,6 +349,18 @@ func WaitLocalProcess(pid int, timeoutSecs uint, initialSignal syscall.Signal, l
 	startTime := time.Now()
 
 	for {
+		var _status syscall.WaitStatus
+		var _rusage syscall.Rusage
+		var waitedPid int
+
+		// "A watched pot never boils" and an unwaited-for process never appears to die!
+		waitedPid, err = syscall.Wait4(pid, &_status, syscall.WNOHANG, &_rusage)
+
+		if waitedPid == pid && err == nil {
+			pidRunning = false
+			break
+		}
+
 		if err = syscall.Kill(pid, syscall.Signal(0)); err != nil {
 			pidRunning = false
 			break