Updated vendored deps

Using github.com/docker/libkv, which is unmaintained, instead of the one
maintained by the original author github.com/abronan/libkv as it has
references to coreos branch.

Fixed directly in vendor a bug in kv/etcd that introduces and error in keys.generated.go

We just delete the file that is rebuilt when build or run getconf:

    $ rm ../vendor/github.com/coreos/etcd/client/keys.generated.go

It is fixed in coreos/etcd master [issues/8715](etcd-io/etcd#8715)
so it will be available in next etcd client release.

Gopkg.toml

@@ -19,8 +19,3 @@
 # [[override]]
 #  name = "github.com/x/y"
 #  version = "2.4.0"
-
-
-[[constraint]]
-  name = "github.com/docker/libkv"
-  version = "0.2.1"

kvstore.go

@@ -7,13 +7,13 @@ import (
 	"strings"
 	"time"
 
-	// "github.com/abronan/libkv"
-	// "github.com/abronan/libkv/store"
-	// "github.com/abronan/libkv/store/consul"
-	// "github.com/abronan/libkv/store/etcd/v3"
 	"github.com/docker/libkv"
 	"github.com/docker/libkv/store"
 	"github.com/docker/libkv/store/consul"
+	"github.com/docker/libkv/store/etcd"
+	// "github.com/abronan/libkv"
+	// "github.com/abronan/libkv/store"
+	// "github.com/abronan/libkv/store/consul"
 	// "github.com/docker/libkv/store/etcd"
 )
 
@@ -69,8 +69,8 @@ func (gc *GetConf) EnableKVStore(opts *KVOptions) (*GetConf, error) {
 			return gc, errors.New("cannot create store consul")
 		}
 		gc.KVStore = kv
-	// case "etcd":
-	// 	etcd.Register()
+	case "etcd":
+		etcd.Register()
 
 	default:
 		return gc, errors.New("unknown backend")