Move supervisor to it's own package

It allows to keep main namespace cleaner

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

supervisor/errors.go

@@ -0,0 +1,24 @@
+package supervisor
+
+import "errors"
+
+var (
+	// External errors
+	ErrEventChanNil           = errors.New("containerd: event channel is nil")
+	ErrBundleNotFound         = errors.New("containerd: bundle not found")
+	ErrContainerNotFound      = errors.New("containerd: container not found")
+	ErrContainerExists        = errors.New("containerd: container already exists")
+	ErrProcessNotFound        = errors.New("containerd: processs not found for container")
+	ErrUnknownContainerStatus = errors.New("containerd: unknown container status ")
+	ErrUnknownEvent           = errors.New("containerd: unknown event type")
+
+	// Internal errors
+	errShutdown          = errors.New("containerd: supervisor is shutdown")
+	errRootNotAbs        = errors.New("containerd: rootfs path is not an absolute path")
+	errNoContainerForPid = errors.New("containerd: pid not registered for any container")
+	// internal error where the handler will defer to another for the final response
+	//
+	// TODO: we could probably do a typed error with another error channel for this to make it
+	// less like magic
+	errDeferedResponse = errors.New("containerd: defered response")
+)