Add only legacy plugins to the legacy lookup map.

Legacy plugin model maintained a map of plugins. This is
not used by the new model. Using this map in the new model
causes incorrect lookup of plugins. This change uses adds
a plugin to the map only if its legacy.

Signed-off-by: Anusha Ragunathan <anusha@docker.com>
Upstream-commit: 8fd779dc28a11d8727d76e9553379b0c854f7c4c
Component: engine

components/engine/pkg/plugins/plugins.go

@@ -83,6 +83,11 @@ func (p *Plugin) Client() *Client {
 	return p.client
 }
 
+// IsLegacy returns true for legacy plugins and false otherwise.
+func (p *Plugin) IsLegacy() bool {
+	return true
+}
+
 // NewLocalPlugin creates a new local plugin.
 func NewLocalPlugin(name, addr string) *Plugin {
 	return &Plugin{