Move proxy and plugin status from shell to Go

In the process we stop printing out the `PLUGIN_FULL_NAME`, but that
is assumed to be something the user can figure out from `docker plugin ls`

plugin/status.go

@@ -0,0 +1,19 @@
+package plugin
+
+type Status struct {
+	DriverName     string
+	MeshDriverName string `json:"MeshDriverName,omitempty"`
+	Version        int
+}
+
+func NewStatus(address, meshAddress string, isPluginV2 bool) *Status {
+	status := &Status{
+		DriverName:     pluginNameFromAddress(address),
+		MeshDriverName: pluginNameFromAddress(meshAddress),
+		Version:        1,
+	}
+	if isPluginV2 {
+		status.Version = 2
+	}
+	return status
+}