MM-8622: Improved plugin error reporting (#8737)

* allow `Wait()`ing on the supervisor

In the event the plugin supervisor shuts down a plugin for crashing too
many times, the new `Wait()` interface allows the `ActivatePlugin` to
accept a callback function to trigger when `supervisor.Wait()` returns.
If the supervisor shuts down normally, this callback is invoked with
a nil error, otherwise any error reported by the supervisor is passed
along.

* improve plugin activation/deactivation logic

Avoid triggering activation of previously failed-to-start plugins just
becase something in the configuration changed. Now, intelligently
compare the global enable bit as well as the each individual plugin's
enabled bit.

* expose store to manipulate PluginStatuses

* expose API to fetch plugin statuses

* keep track of whether or not plugin sandboxing is supported

* transition plugin statuses

* restore error on plugin activation if already active

* don't initialize test plugins until successfully loaded

* emit websocket events when plugin statuses change

* skip pruning if already initialized

* MM-8622: maintain plugin statuses in memory

Switch away from persisting plugin statuses to the database, and
maintain in memory instead. This will be followed by a cluster interface
to query the in-memory status of plugin statuses from all cluster nodes.

At the same time, rename `cluster_discovery_id` on the `PluginStatus`
model object to `cluster_id`.

* MM-8622: aggregate plugin statuses across cluster

* fetch cluster plugin statuses when emitting websocket notification

* address unit test fixes after rebasing

* relax (poor) racey unit test re: supervisor.Wait()

* make store-mocks

plugin/pluginenv/environment_test.go

@@ -56,6 +56,10 @@ func (m *MockSupervisor) Hooks() plugin.Hooks {
 	return m.Called().Get(0).(plugin.Hooks)
 }
 
+func (m *MockSupervisor) Wait() error {
+	return m.Called().Get(0).(error)
+}
+
 func initTmpDir(t *testing.T, files map[string]string) string {
 	success := false
 	dir, err := ioutil.TempDir("", "mm-plugin-test")
@@ -130,7 +134,7 @@ func TestEnvironment(t *testing.T) {
 	activePlugins := env.ActivePlugins()
 	assert.Len(t, activePlugins, 0)
 
-	assert.Error(t, env.ActivatePlugin("x"))
+	assert.Error(t, env.ActivatePlugin("x", nil))
 
 	var api struct{ plugin.API }
 	var supervisor MockSupervisor
@@ -145,11 +149,11 @@ func TestEnvironment(t *testing.T) {
 	supervisor.On("Stop").Return(nil)
 	supervisor.On("Hooks").Return(&hooks)
 
-	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.NoError(t, env.ActivatePlugin("foo", nil))
 	assert.Equal(t, env.ActivePluginIds(), []string{"foo"})
 	activePlugins = env.ActivePlugins()
 	assert.Len(t, activePlugins, 1)
-	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.Error(t, env.ActivatePlugin("foo", nil))
 	assert.True(t, env.IsPluginActive("foo"))
 
 	hooks.On("OnDeactivate").Return(nil)
@@ -157,7 +161,7 @@ func TestEnvironment(t *testing.T) {
 	assert.Error(t, env.DeactivatePlugin("foo"))
 	assert.False(t, env.IsPluginActive("foo"))
 
-	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.NoError(t, env.ActivatePlugin("foo", nil))
 	assert.Equal(t, env.ActivePluginIds(), []string{"foo"})
 
 	assert.Equal(t, env.SearchPath(), dir)
@@ -184,7 +188,7 @@ func TestEnvironment_DuplicatePluginError(t *testing.T) {
 	require.NoError(t, err)
 	defer env.Shutdown()
 
-	assert.Error(t, env.ActivatePlugin("foo"))
+	assert.Error(t, env.ActivatePlugin("foo", nil))
 	assert.Empty(t, env.ActivePluginIds())
 }
 
@@ -200,7 +204,7 @@ func TestEnvironment_BadSearchPathError(t *testing.T) {
 	require.NoError(t, err)
 	defer env.Shutdown()
 
-	assert.Error(t, env.ActivatePlugin("foo"))
+	assert.Error(t, env.ActivatePlugin("foo", nil))
 	assert.Empty(t, env.ActivePluginIds())
 }
 
@@ -244,7 +248,7 @@ func TestEnvironment_ActivatePluginErrors(t *testing.T) {
 			hooks.Mock = mock.Mock{}
 			provider.Mock = mock.Mock{}
 			setup()
-			assert.Error(t, env.ActivatePlugin("foo"))
+			assert.Error(t, env.ActivatePlugin("foo", nil))
 			assert.Empty(t, env.ActivePluginIds())
 			supervisor.AssertExpectations(t)
 			hooks.AssertExpectations(t)
@@ -285,7 +289,7 @@ func TestEnvironment_ShutdownError(t *testing.T) {
 
 	hooks.On("OnDeactivate").Return(fmt.Errorf("test error"))
 
-	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.NoError(t, env.ActivatePlugin("foo", nil))
 	assert.Equal(t, env.ActivePluginIds(), []string{"foo"})
 	assert.Len(t, env.Shutdown(), 2)
 }
@@ -332,7 +336,7 @@ func TestEnvironment_ConcurrentHookInvocations(t *testing.T) {
 		}
 	})
 
-	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.NoError(t, env.ActivatePlugin("foo", nil))
 
 	rec := httptest.NewRecorder()
 
@@ -391,7 +395,7 @@ func TestEnvironment_HooksForPlugins(t *testing.T) {
 		Text: "bar",
 	}, nil)
 
-	assert.NoError(t, env.ActivatePlugin("foo"))
+	assert.NoError(t, env.ActivatePlugin("foo", nil))
 	assert.Equal(t, env.ActivePluginIds(), []string{"foo"})
 
 	resp, appErr, err := env.HooksForPlugin("foo").ExecuteCommand(&model.CommandArgs{