MM-10702 Moving plugins to use hashicorp go-plugin. (#8978)

* Moving plugins to use hashicorp go-plugin.

* Tweaks from feedback.

migrations/migrationstestlib.go

@@ -4,19 +4,15 @@
 package migrations
 
 import (
-	"encoding/json"
 	"io"
 	"io/ioutil"
 	"os"
-	"path/filepath"
 	"time"
 
 	"github.com/mattermost/mattermost-server/app"
 	"github.com/mattermost/mattermost-server/einterfaces"
 	"github.com/mattermost/mattermost-server/mlog"
 	"github.com/mattermost/mattermost-server/model"
-	"github.com/mattermost/mattermost-server/plugin"
-	"github.com/mattermost/mattermost-server/plugin/pluginenv"
 	"github.com/mattermost/mattermost-server/store"
 	"github.com/mattermost/mattermost-server/store/sqlstore"
 	"github.com/mattermost/mattermost-server/store/storetest"
@@ -35,7 +31,6 @@ type TestHelper struct {
 
 	tempConfigPath string
 	tempWorkspace  string
-	pluginHooks    map[string]plugin.Hooks
 }
 
 type persistentTestStore struct {
@@ -93,7 +88,6 @@ func setupTestHelper(enterprise bool) *TestHelper {
 
 	th := &TestHelper{
 		App:            a,
-		pluginHooks:    make(map[string]plugin.Hooks),
 		tempConfigPath: tempConfig.Name(),
 	}
 
@@ -307,62 +301,6 @@ func (me *TestHelper) TearDown() {
 	}
 }
 
-type mockPluginSupervisor struct {
-	hooks plugin.Hooks
-}
-
-func (s *mockPluginSupervisor) Start(api plugin.API) error {
-	return s.hooks.OnActivate(api)
-}
-
-func (s *mockPluginSupervisor) Stop() error {
-	return nil
-}
-
-func (s *mockPluginSupervisor) Hooks() plugin.Hooks {
-	return s.hooks
-}
-
-func (s *mockPluginSupervisor) Wait() error { return nil }
-
-func (me *TestHelper) InstallPlugin(manifest *model.Manifest, hooks plugin.Hooks) {
-	if me.tempWorkspace == "" {
-		dir, err := ioutil.TempDir("", "apptest")
-		if err != nil {
-			panic(err)
-		}
-		me.tempWorkspace = dir
-	}
-
-	pluginDir := filepath.Join(me.tempWorkspace, "plugins")
-	webappDir := filepath.Join(me.tempWorkspace, "webapp")
-	me.App.InitPlugins(pluginDir, webappDir, func(bundle *model.BundleInfo) (plugin.Supervisor, error) {
-		if hooks, ok := me.pluginHooks[bundle.Manifest.Id]; ok {
-			return &mockPluginSupervisor{hooks}, nil
-		}
-		return pluginenv.DefaultSupervisorProvider(bundle)
-	})
-
-	me.pluginHooks[manifest.Id] = hooks
-
-	manifestCopy := *manifest
-	if manifestCopy.Backend == nil {
-		manifestCopy.Backend = &model.ManifestBackend{}
-	}
-	manifestBytes, err := json.Marshal(&manifestCopy)
-	if err != nil {
-		panic(err)
-	}
-
-	if err := os.MkdirAll(filepath.Join(pluginDir, manifest.Id), 0700); err != nil {
-		panic(err)
-	}
-
-	if err := ioutil.WriteFile(filepath.Join(pluginDir, manifest.Id, "plugin.json"), manifestBytes, 0600); err != nil {
-		panic(err)
-	}
-}
-
 func (me *TestHelper) ResetRoleMigration() {
 	if _, err := testStoreSqlSupplier.GetMaster().Exec("DELETE from Roles"); err != nil {
 		panic(err)