Use CombinedOutput in vm_test

Signed-off-by: Ronald G Minnich <rminnich@gmail.com>

Author: rminnich

initramfs/vm_test.go

@@ -9,7 +9,6 @@ package initramfs_test
 import (
 	"context"
 	"errors"
-	"io"
 	"os"
 	"path/filepath"
 	"testing"
@@ -60,17 +59,11 @@ func TestCPU(t *testing.T) {
 			t.Fatalf("CPUCommand: got %v, want nil", err)
 		}
 		client.SetVerbose(t.Logf)
-		r, w, err := os.Pipe()
-		cpu.Stdout, cpu.Stderr = w, w
 
-		err = cpu.Run()
+		b, err := cpu.CombinedOutput()
 		if err == nil != tt.ok {
 			t.Errorf("%s %s: got %v, want %v", tt.cmd, tt.args, err == nil != tt.ok, err == nil == tt.ok)
 		}
-		b, err := io.ReadAll(r)
-		if err != nil {
-			t.Errorf("reading pipe output: got %v, want nil", err)
-		}
 		t.Logf("%q", string(b))
 	}
 	b, err := os.ReadFile(filepath.Join(d, "b"))