remove old raft servers if they don't answer to pings for too long (#3398)

* remove old raft servers if they don't answer to pings for too long

add ping durations as options

rename ping fields

fix some todos

get masters through masterclient

raft remove server from leader

use raft servers to ping them

CheckMastersAlive for hashicorp raft only

* prepare blocking ping

* pass waitForReady as param

* pass waitForReady through all functions

* waitForReady works

* refactor

* remove unneeded params

* rollback unneeded changes

* fix

weed/shell/command_collection_delete.go

@@ -4,8 +4,9 @@ import (
 	"context"
 	"flag"
 	"fmt"
-	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
 	"io"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
 )
 
 func init() {