windows/svc: use wevtutil.exe instead of powershell for windows/arm

Use wevtutil.exe to query event log instead of powershell's Get-EventLog
command, which is not available on Windows IoT Core.

Updates golang/go#26148

Change-Id: Idc16d0b18d2826730d2b4062388b2a764c4886c6
Reviewed-on: https://go-review.googlesource.com/c/154817
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

windows/svc/svc_test.go

@@ -121,13 +121,9 @@ func TestExample(t *testing.T) {
 		t.Fatalf("Delete failed: %s", err)
 	}
 
-	cmd := `Get-Eventlog -LogName Application -Newest 100` +
-		` | Where Source -eq "myservice"` +
-		` | Select -first 10` +
-		` | Format-table -HideTableHeaders -property ReplacementStrings`
-	out, err := exec.Command("powershell", "-Command", cmd).CombinedOutput()
+	out, err := exec.Command("wevtutil.exe", "qe", "Application", "/q:*[System[Provider[@Name='myservice']]]", "/rd:true", "/c:10").CombinedOutput()
 	if err != nil {
-		t.Fatalf("powershell failed: %v\n%v", err, string(out))
+		t.Fatalf("wevtutil failed: %v\n%v", err, string(out))
 	}
 	if want := strings.Join(append([]string{name}, args...), "-"); !strings.Contains(string(out), want) {
 		t.Errorf("%q string does not contain %q", string(out), want)