Setup plugin ids and dependencies

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

snapshot/btrfs/btrfs.go

@@ -20,11 +20,11 @@ import (
 )
 
 func init() {
-	plugin.Register("snapshot-btrfs", &plugin.Registration{
+	plugin.Register(&plugin.Registration{
+		ID:   "btrfs",
 		Type: plugin.SnapshotPlugin,
 		Init: func(ic *plugin.InitContext) (interface{}, error) {
-			root := filepath.Join(ic.Root, "snapshot", "btrfs")
-			return NewSnapshotter(root)
+			return NewSnapshotter(ic.Root)
 		},
 	})
 }

snapshot/naive/naive.go

@@ -16,10 +16,11 @@ import (
 )
 
 func init() {
-	plugin.Register("snapshot-naive", &plugin.Registration{
+	plugin.Register(&plugin.Registration{
 		Type: plugin.SnapshotPlugin,
+		ID:   "naive",
 		Init: func(ic *plugin.InitContext) (interface{}, error) {
-			return NewSnapshotter(filepath.Join(ic.Root, "snapshot", "naive"))
+			return NewSnapshotter(ic.Root)
 		},
 	})
 }

snapshot/overlay/overlay.go

@@ -20,10 +20,11 @@ import (
 )
 
 func init() {
-	plugin.Register("snapshot-overlay", &plugin.Registration{
+	plugin.Register(&plugin.Registration{
 		Type: plugin.SnapshotPlugin,
+		ID:   "overlayfs",
 		Init: func(ic *plugin.InitContext) (interface{}, error) {
-			return NewSnapshotter(filepath.Join(ic.Root, "snapshot", "overlay"))
+			return NewSnapshotter(ic.Root)
 		},
 	})
 }

snapshot/windows/windows.go

@@ -4,7 +4,6 @@ package windows
 
 import (
 	"context"
-	"path/filepath"
 
 	"github.com/containerd/containerd/mount"
 	"github.com/containerd/containerd/plugin"
@@ -17,10 +16,11 @@ var (
 )
 
 func init() {
-	plugin.Register("snapshot-windows", &plugin.Registration{
+	plugin.Register(&plugin.Registration{
 		Type: plugin.SnapshotPlugin,
+		ID:   "windows",
 		Init: func(ic *plugin.InitContext) (interface{}, error) {
-			return NewSnapshotter(filepath.Join(ic.Root, "snapshot", "windows"))
+			return NewSnapshotter(ic.Root)
 		},
 	})
 }