filer store adds kv support

can compile now, need to implement those unimplemented

weed/filer/etcd/etcd_store_kv.go

@@ -0,0 +1,44 @@
+package etcd
+
+import (
+	"context"
+	"fmt"
+	"github.com/chrislusf/seaweedfs/weed/filer"
+)
+
+func (store *EtcdStore) KvPut(ctx context.Context, key []byte, value []byte) (err error) {
+
+	_, err = store.client.Put(ctx, string(key), string(value))
+
+	if err != nil {
+		return fmt.Errorf("kv put: %v", err)
+	}
+
+	return nil
+}
+
+func (store *EtcdStore) KvGet(ctx context.Context, key []byte) (value []byte, err error) {
+
+	resp, err := store.client.Get(ctx, string(key), nil)
+
+	if err != nil {
+		return nil, fmt.Errorf("kv get: %v", err)
+	}
+
+	if len(resp.Kvs) == 0 {
+		return nil, filer.ErrKvNotFound
+	}
+
+	return resp.Kvs[0].Value, nil
+}
+
+func (store *EtcdStore) KvDelete(ctx context.Context, key []byte) (err error) {
+
+	_, err = store.client.Delete(ctx, string(key))
+
+	if err != nil {
+		return fmt.Errorf("kv delete: %v", err)
+	}
+
+	return nil
+}