Add plugin backend reload capability (#3112)

* Add plugin reload capability on all mounts for a specific plugin type

* Comments cleanup

* Add per-mount plugin backend reload, add tests

* Fix typos

* Remove old comment

* Reuse existing storage view in reloadPluginCommon

* Correctly handle reloading auth plugin backends

* Update path to plugin/backend/reload

* Use multierrors on reloadMatchingPluginMounts, attempt to reload all mounts provided

* Use internal value as check to ensure plugin backend reload

* Remove connection state from request for plugins at the moment

* Minor cleanup

* Refactor tests

logical/plugin/mock/path_internal.go

@@ -9,15 +9,26 @@ import (
 // it is used to test the invalidate func.
 func pathInternal(b *backend) *framework.Path {
 	return &framework.Path{
-		Pattern:        "internal",
-		Fields:         map[string]*framework.FieldSchema{},
-		ExistenceCheck: b.pathExistenceCheck,
+		Pattern: "internal",
+		Fields: map[string]*framework.FieldSchema{
+			"value": &framework.FieldSchema{Type: framework.TypeString},
+		},
 		Callbacks: map[logical.Operation]framework.OperationFunc{
-			logical.ReadOperation: b.pathInternalRead,
+			logical.UpdateOperation: b.pathInternalUpdate,
+			logical.ReadOperation:   b.pathInternalRead,
 		},
 	}
 }
 
+func (b *backend) pathInternalUpdate(
+	req *logical.Request, data *framework.FieldData) (*logical.Response, error) {
+	value := data.Get("value").(string)
+	b.internal = value
+	// Return the secret
+	return nil, nil
+
+}
+
 func (b *backend) pathInternalRead(
 	req *logical.Request, data *framework.FieldData) (*logical.Response, error) {
 	// Return the secret