Remove kubelet dependency on pkill

Issue #26093 identified pkill as one of the dependencies of kublet
which could be worked around.  Build on the code introduced for pidof
and regexp for the process(es) we need to send a signal to.

Related to #26093

pkg/util/procfs/procfs_test.go

@@ -19,9 +19,12 @@ package procfs
 import (
 	"io/ioutil"
 	"os"
+	"os/signal"
 	"path/filepath"
 	"runtime"
+	"syscall"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -66,7 +69,27 @@ func TestPidOf(t *testing.T) {
 	if runtime.GOOS == "darwin" || runtime.GOOS == "windows" {
 		t.Skipf("not supported on GOOS=%s", runtime.GOOS)
 	}
-	pids := PidOf(filepath.Base(os.Args[0]))
+	pids, err := PidOf(filepath.Base(os.Args[0]))
+	assert.Empty(t, err)
 	assert.NotZero(t, pids)
 	assert.Contains(t, pids, os.Getpid())
 }
+
+func TestPKill(t *testing.T) {
+	if runtime.GOOS == "darwin" || runtime.GOOS == "windows" {
+		t.Skipf("not supported on GOOS=%s", runtime.GOOS)
+	}
+	sig := syscall.SIGCONT
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, sig)
+	defer signal.Stop(c)
+	PKill(os.Args[0], sig)
+	select {
+	case s := <-c:
+		if s != sig {
+			t.Fatalf("signal was %v, want %v", s, sig)
+		}
+	case <-time.After(1 * time.Second):
+		t.Fatalf("timeout waiting for %v", sig)
+	}
+}