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

1 files changed, 1 insertions, 1 deletions

diff --git a/model/cluster_discovery.go b/model/cluster_discovery.go
index 89e5fc95e..5d5b0465d 100644
--- a/model/cluster_discovery.go
+++ b/model/cluster_discovery.go
@@ -86,7 +86,7 @@ func FilterClusterDiscovery(vs []*ClusterDiscovery, f func(*ClusterDiscovery) bo
 
 func (o *ClusterDiscovery) IsValid() *AppError {
 	if len(o.Id) != 26 {
-		return NewAppError("Channel.IsValid", "model.channel.is_valid.id.app_error", nil, "", http.StatusBadRequest)
+		return NewAppError("ClusterDiscovery.IsValid", "model.cluster.is_valid.id.app_error", nil, "", http.StatusBadRequest)
 	}
 
 	if len(o.ClusterName) == 0 {