use libnetwork/slirp4netns from c/common

Most of the code moved there so if from there and remove it here.

Some extra changes are required here. This is a bit of a mess. The pipe
handling makes this a bit more difficult.

[NO NEW TESTS NEEDED] This is just a rework, existing tests must pass.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

vendor/github.com/containers/common/pkg/servicereaper/service.go

@@ -0,0 +1,65 @@
+//go:build linux
+// +build linux
+
+package servicereaper
+
+import (
+	"os"
+	"os/signal"
+	"sync"
+	"syscall"
+
+	"github.com/sirupsen/logrus"
+)
+
+type service struct {
+	pidMap map[int]bool
+	mutex  *sync.Mutex
+}
+
+var s = service{
+	pidMap: map[int]bool{},
+	mutex:  &sync.Mutex{},
+}
+
+func AddPID(pid int) {
+	s.mutex.Lock()
+	s.pidMap[pid] = true
+	s.mutex.Unlock()
+}
+
+func Start() {
+	// create signal channel and only wait for SIGCHLD
+	sigc := make(chan os.Signal, 1)
+	signal.Notify(sigc, syscall.SIGCHLD)
+	// wait and reap in an  extra goroutine
+	go reaper(sigc)
+}
+
+func reaper(sigc chan os.Signal) {
+	for {
+		// block until we receive SIGCHLD
+		<-sigc
+		s.mutex.Lock()
+		for pid := range s.pidMap {
+			var status syscall.WaitStatus
+			waitpid, err := syscall.Wait4(pid, &status, syscall.WNOHANG, nil)
+			if err != nil {
+				// do not log error for ECHILD
+				if err != syscall.ECHILD {
+					logrus.Warnf("Wait for pid %d failed: %v ", pid, err)
+				}
+				delete(s.pidMap, pid)
+				continue
+			}
+			// if pid == 0 nothing happened
+			if waitpid == 0 {
+				continue
+			}
+			if status.Exited() || status.Signaled() {
+				delete(s.pidMap, pid)
+			}
+		}
+		s.mutex.Unlock()
+	}
+}