add PKCS11 support (#1153)

* add PKCS11 support

* add pkcs11 build option to the makefile, add a stub pkclient to avoid forcing CGO onto people

* don't print the pkcs11 option on nebula-cert keygen if not compiled in

* remove linux-arm64-pkcs11 from the all target to fix CI

* correctly serialize ec keys

* nebula-cert: support PKCS#11 for sign and ca

* fix gofmt lint

* clean up some logic with regard to closing sessions

* pkclient: handle empty correctly for TPM2

* Update Makefile and Actions

---------

Co-authored-by: Morgan Jones <me@numin.it>
Co-authored-by: John Maguire <contact@johnmaguire.me>

cmd/nebula-cert/main_test.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"io"
 	"os"
 	"testing"
@@ -77,8 +78,16 @@ func assertHelpError(t *testing.T, err error, msg string) {
 	case *helpError:
 		// good
 	default:
-		t.Fatal("err was not a helpError")
+		t.Fatal(fmt.Sprintf("err was not a helpError: %q, expected %q", err, msg))
 	}
 
 	assert.EqualError(t, err, msg)
 }
+
+func optionalPkcs11String(msg string) string {
+	if p11Supported() {
+		return msg
+	} else {
+		return ""
+	}
+}