server/vault: tweak error messages

Closes #5139

nomad/vault.go

@@ -438,7 +438,7 @@ OUTER:
 				retryTimer.Reset(v.config.ConnectionRetryIntv)
 				v.l.Lock()
 				v.connEstablished = true
-				v.connEstablishedErr = fmt.Errorf("Nomad Server failed to establish connections to Vault: %v", err)
+				v.connEstablishedErr = fmt.Errorf("failed to establish connections to Vault: %v", err)
 				v.l.Unlock()
 				continue OUTER
 			}
@@ -517,7 +517,8 @@ func (v *vaultClient) renewalLoop() {
 			if backoff < 0 {
 				// We have failed to renew the token past its expiration. Stop
 				// renewing with Vault.
-				v.logger.Error("failed to renew Vault token before lease expiration. Shutting down Vault client")
+				v.logger.Error("failed to renew Vault token before lease expiration. Shutting down Vault client",
+					"error", err)
 				v.l.Lock()
 				v.connEstablished = false
 				v.connEstablishedErr = err
@@ -905,7 +906,7 @@ func (v *vaultClient) CreateToken(ctx context.Context, a *structs.Allocation, ta
 	if established, err := v.ConnectionEstablished(); !established && err == nil {
 		return nil, structs.NewRecoverableError(fmt.Errorf("Connection to Vault has not been established"), true)
 	} else if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("failed to establish connection to Vault", err)
 	}
 
 	// Track how long the request takes