token-server: Fix panic when generating machine token for unrecognized machine.

tokenserver/appengine/impl/machinetoken/bigquery_log_test.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package machinetoken
 
 import (
         "net"
         "testing"
         "time"
 
         "github.com/luci/luci-go/common/clock"
         "github.com/luci/luci-go/common/proto/google"
         "github.com/luci/luci-go/tokenserver/api"
         "github.com/luci/luci-go/tokenserver/api/minter/v1"
 
         . "github.com/smartystreets/goconvey/convey"
 )
 
 func TestMintedTokenInfo(t *testing.T) {
         Convey("produces correct row map", t, func() {
-                ctx := testingContext()
+                ctx := testingContext(testingCA)

[smut, 2017/06/20 22:37:17]

Where is testingCA defined?

 
                 info := MintedTokenInfo{
                         Request: testingRawRequest(ctx),
                         Response: &minter.MachineTokenResponse{
                                 ServiceVersion: "unit-tests/mocked-ver",
                                 TokenType: &minter.MachineTokenResponse_LuciMachineToken{
                                         LuciMachineToken: &minter.LuciMachineToken{
                                                 MachineToken: "zzzz",
                                                 Expiry:       google.NewTimestamp(clock.Now(ctx).Add(time.Hour)),
                                         },
@@ skipping 21 matching lines @@
                         "gae_request_id":      "gae-request-id",
                         "issued_at":           1.422936306e+09,
                         "machine_fqdn":        "luci-token-server-test-1.fake.domain",
                         "peer_ip":             "127.10.10.10",
                         "service_version":     "unit-tests/mocked-ver",
                         "signature_algorithm": "SHA256_RSA_ALGO",
                         "token_type":          "LUCI_MACHINE_TOKEN",
                 })
         })
 }