*: add support for lease create and revoke

Basic support for lease operations like create and revoke.
We still need to:
1. attach keys to leases in KV implmentation if lease field is set
2. leader periodically removes expired leases
3. leader serves keepAlive requests and follower forwards keepAlive
requests to leader.

etcdserver/server.go

@@ -34,6 +34,7 @@ import (
 	"github.com/coreos/etcd/etcdserver/etcdhttp/httptypes"
 	pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
 	"github.com/coreos/etcd/etcdserver/stats"
+	"github.com/coreos/etcd/lease"
 	"github.com/coreos/etcd/pkg/fileutil"
 	"github.com/coreos/etcd/pkg/idutil"
 	"github.com/coreos/etcd/pkg/pbutil"
@@ -166,8 +167,9 @@ type EtcdServer struct {
 
 	store store.Store
 
-	kv dstorage.ConsistentWatchableKV
-	be backend.Backend
+	kv     dstorage.ConsistentWatchableKV
+	lessor lease.Lessor
+	be     backend.Backend
 
 	stats  *stats.ServerStats
 	lstats *stats.LeaderStats
@@ -360,6 +362,7 @@ func NewServer(cfg *ServerConfig) (*EtcdServer, error) {
 	if cfg.V3demo {
 		srv.be = backend.NewDefaultBackend(path.Join(cfg.SnapDir(), databaseFilename))
 		srv.kv = dstorage.New(srv.be, &srv.consistIndex)
+		srv.lessor = lease.NewLessor(uint8(id), srv.be, srv.kv)
 	}
 
 	// TODO: move transport initialization near the definition of remote
@@ -589,6 +592,8 @@ func (s *EtcdServer) applySnapshot(ep *etcdProgress, apply *apply) {
 			plog.Panicf("rename snapshot file error: %v", err)
 		}
 
+		// TODO: recover leassor
+
 		newbe := backend.NewDefaultBackend(fn)
 		if err := s.kv.Restore(newbe); err != nil {
 			plog.Panicf("restore KV error: %v", err)