feat(worker): Implemented docker executor, close #55

if docker is enabled in configure file and `docker_image` is set on mirror config, the command would

be executed via `docker run ...`

worker/base_provider.go

@@ -24,7 +24,9 @@ type baseProvider struct {
 
 	cgroup *cgroupHook
 	zfs    *zfsHook
-	hooks  []jobHook
+	docker *dockerHook
+
+	hooks []jobHook
 }
 
 func (p *baseProvider) Name() string {
@@ -87,6 +89,8 @@ func (p *baseProvider) AddHook(hook jobHook) {
 		p.cgroup = v
 	case *zfsHook:
 		p.zfs = v
+	case *dockerHook:
+		p.docker = v
 	}
 	p.hooks = append(p.hooks, hook)
 }
@@ -103,6 +107,10 @@ func (p *baseProvider) ZFS() *zfsHook {
 	return p.zfs
 }
 
+func (p *baseProvider) Docker() *dockerHook {
+	return p.docker
+}
+
 func (p *baseProvider) prepareLogFile() error {
 	if p.LogFile() == "/dev/null" {
 		p.cmd.SetLogFile(nil)