test: fix concurrent map access when setting up test vault

agent/connect/ca/provider_vault_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net"
+	"sync"
 	"testing"
 	"time"
 
@@ -16,11 +17,16 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+var vaultLock sync.Mutex
+
 func testVaultCluster(t *testing.T) (*VaultProvider, *vault.Core, net.Listener) {
 	return testVaultClusterWithConfig(t, true, nil)
 }
 
 func testVaultClusterWithConfig(t *testing.T, isRoot bool, rawConf map[string]interface{}) (*VaultProvider, *vault.Core, net.Listener) {
+	vaultLock.Lock()
+	defer vaultLock.Unlock()
+
 	if err := vault.AddTestLogicalBackend("pki", pki.Factory); err != nil {
 		t.Fatal(err)
 	}