enhance: split config from server package

The github.com/containerd/containerd/services/server has a lot of
dependencies, like content, snapshots services implementation and
docker-metrics.

For the client side, it uses the config struct from server package
to start up the containerd in background. It will import a lot of
useless packages which might be conflict with existing vendor's package.

It makes integration easier with single config package.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

cmd/containerd/command/config_linux.go

@@ -18,14 +18,14 @@ package command
 
 import (
 	"github.com/containerd/containerd/defaults"
-	"github.com/containerd/containerd/services/server"
+	srvconfig "github.com/containerd/containerd/services/server/config"
 )
 
-func defaultConfig() *server.Config {
-	return &server.Config{
+func defaultConfig() *srvconfig.Config {
+	return &srvconfig.Config{
 		Root:  defaults.DefaultRootDir,
 		State: defaults.DefaultStateDir,
-		GRPC: server.GRPCConfig{
+		GRPC: srvconfig.GRPCConfig{
 			Address:        defaults.DefaultAddress,
 			MaxRecvMsgSize: defaults.DefaultMaxRecvMsgSize,
 			MaxSendMsgSize: defaults.DefaultMaxSendMsgSize,