add --connector switch, validation

connector/docker.go

@@ -19,7 +19,7 @@ type Docker struct {
 	lock         sync.RWMutex
 }
 
-func NewDocker() *Docker {
+func NewDocker() Connector {
 	// init docker client
 	client, err := api.NewClientFromEnv()
 	if err != nil {

connector/main.go

@@ -7,7 +7,7 @@ import (
 
 var log = logging.Init()
 
-type ContainerSource interface {
+type Connector interface {
 	All() container.Containers
 	Get(string) (*container.Container, bool)
 }

connector/runc.go

@@ -59,7 +59,7 @@ func getFactory(opts RuncOpts) (libcontainer.Factory, error) {
 	return libcontainer.New(opts.root, cgroupManager, libcontainer.CriuPath("criu"))
 }
 
-func NewRunc() *Runc {
+func NewRunc() Connector {
 	opts, err := readRuncOpts()
 	runcFailOnErr(err)