cmd: migrate to urfave/cli/v2 (#24751)

This change updates our urfave/cli dependency to the v2 branch of the library.
There are some Go API changes in cli v2:

- Flag values can now be accessed using the methods ctx.Bool,
  ctx.Int, ctx.String, ... regardless of whether the flag is 'local' or
  'global'.

- v2 has built-in support for flag categories. Our home-grown category
  system is removed and the categories of flags are assigned as part of
  the flag definition.

For users, there is only one observable difference with cli v2: flags must now
strictly appear before regular arguments. For example, the following command is
now invalid:

   geth account import mykey.json --password file.txt

Instead, the command must be invoked as follows:

   geth account import --password file.txt mykey.json

cmd/utils/cmd.go

@@ -41,7 +41,7 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/node"
 	"github.com/ethereum/go-ethereum/rlp"
-	"gopkg.in/urfave/cli.v1"
+	"github.com/urfave/cli/v2"
 )
 
 const (
@@ -78,10 +78,10 @@ func StartNode(ctx *cli.Context, stack *node.Node, isConsole bool) {
 		defer signal.Stop(sigc)
 
 		minFreeDiskSpace := 2 * ethconfig.Defaults.TrieDirtyCache // Default 2 * 256Mb
-		if ctx.GlobalIsSet(MinFreeDiskSpaceFlag.Name) {
-			minFreeDiskSpace = ctx.GlobalInt(MinFreeDiskSpaceFlag.Name)
-		} else if ctx.GlobalIsSet(CacheFlag.Name) || ctx.GlobalIsSet(CacheGCFlag.Name) {
-			minFreeDiskSpace = 2 * ctx.GlobalInt(CacheFlag.Name) * ctx.GlobalInt(CacheGCFlag.Name) / 100
+		if ctx.IsSet(MinFreeDiskSpaceFlag.Name) {
+			minFreeDiskSpace = ctx.Int(MinFreeDiskSpaceFlag.Name)
+		} else if ctx.IsSet(CacheFlag.Name) || ctx.IsSet(CacheGCFlag.Name) {
+			minFreeDiskSpace = 2 * ctx.Int(CacheFlag.Name) * ctx.Int(CacheGCFlag.Name) / 100
 		}
 		if minFreeDiskSpace > 0 {
 			go monitorFreeDiskSpace(sigc, stack.InstanceDir(), uint64(minFreeDiskSpace)*1024*1024)