cmd/swarm/swarm-snapshot: swarm snapshot generator (#18453)

* cmd/swarm/swarm-snapshot: add binary to create network snapshots

* cmd/swarm/swarm-snapshot: refactor and extend tests

* p2p/simulations: remove unused triggerChecks func and fix linter

* internal/cmdtest: raise the timeout for killing TestCmd

* cmd/swarm/swarm-snapshot: add more comments and other minor adjustments

* cmd/swarm/swarm-snapshot: remove redundant check in createSnapshot

* cmd/swarm/swarm-snapshot: change comment wording

* p2p/simulations: revert Simulation.Run from master

https://github.com/ethersphere/go-ethereum/pull/1077/files#r247078904

* cmd/swarm/swarm-snapshot: address pr comments

* swarm/network/simulations/discovery: removed snapshot write to file

* cmd/swarm/swarm-snapshot, swarm/network/simulations: removed redundant connection event check, fixed lint error

cmd/swarm/swarm-snapshot/main.go

@@ -0,0 +1,82 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"os"
+
+	"github.com/ethereum/go-ethereum/cmd/utils"
+	"github.com/ethereum/go-ethereum/log"
+	cli "gopkg.in/urfave/cli.v1"
+)
+
+var gitCommit string // Git SHA1 commit hash of the release (set via linker flags)
+
+// default value for "create" command --nodes flag
+const defaultNodes = 10
+
+func main() {
+	err := newApp().Run(os.Args)
+	if err != nil {
+		log.Error(err.Error())
+		os.Exit(1)
+	}
+}
+
+// newApp construct a new instance of Swarm Snapshot Utility.
+// Method Run is called on it in the main function and in tests.
+func newApp() (app *cli.App) {
+	app = utils.NewApp(gitCommit, "Swarm Snapshot Utility")
+
+	app.Name = "swarm-snapshot"
+	app.Usage = ""
+
+	// app flags (for all commands)
+	app.Flags = []cli.Flag{
+		cli.IntFlag{
+			Name:  "verbosity",
+			Value: 1,
+			Usage: "verbosity level",
+		},
+	}
+
+	app.Commands = []cli.Command{
+		{
+			Name:    "create",
+			Aliases: []string{"c"},
+			Usage:   "create a swarm snapshot",
+			Action:  create,
+			// Flags only for "create" command.
+			// Allow app flags to be specified after the
+			// command argument.
+			Flags: append(app.Flags,
+				cli.IntFlag{
+					Name:  "nodes",
+					Value: defaultNodes,
+					Usage: "number of nodes",
+				},
+				cli.StringFlag{
+					Name:  "services",
+					Value: "bzz",
+					Usage: "comma separated list of services to boot the nodes with",
+				},
+			),
+		},
+	}
+
+	return app
+}