avoid grpc 5 seconds timeout

some operations may take longer than 5 seconds.

only keep the timeout for raft operations

weed/server/master_server_handlers_admin.go

@@ -4,17 +4,15 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"math/rand"
-	"net/http"
-	"strconv"
-	"time"
-
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/operation"
 	"github.com/chrislusf/seaweedfs/weed/pb/volume_server_pb"
 	"github.com/chrislusf/seaweedfs/weed/storage"
 	"github.com/chrislusf/seaweedfs/weed/topology"
 	"github.com/chrislusf/seaweedfs/weed/util"
+	"math/rand"
+	"net/http"
+	"strconv"
 )
 
 func (ms *MasterServer) collectionDeleteHandler(w http.ResponseWriter, r *http.Request) {
@@ -25,10 +23,7 @@ func (ms *MasterServer) collectionDeleteHandler(w http.ResponseWriter, r *http.R
 	}
 	for _, server := range collection.ListVolumeServers() {
 		err := operation.WithVolumeServerClient(server.Url(), ms.grpcDialOpiton, func(client volume_server_pb.VolumeServerClient) error {
-			ctx, cancel := context.WithTimeout(context.Background(), time.Duration(5*time.Second))
-			defer cancel()
-
-			_, deleteErr := client.DeleteCollection(ctx, &volume_server_pb.DeleteCollectionRequest{
+			_, deleteErr := client.DeleteCollection(context.Background(), &volume_server_pb.DeleteCollectionRequest{
 				Collection: collection.Name,
 			})
 			return deleteErr