Support podman-remote stop container(s)

* Clean up adapter code
* Add GetContainersByContext to Varlink API
* Add missing comments
* Restore save command
* Restore error type mapping when using varlink

Signed-off-by: Jhon Honce <jhonce@redhat.com>

cmd/podman/main.go

@@ -49,6 +49,7 @@ var mainCommands = []*cobra.Command{
 	_pushCommand,
 	&_rmiCommand,
 	_saveCommand,
+	_stopCommand,
 	_tagCommand,
 	_versionCommand,
 	imageCommand.Command,