Add ctl tool for Raft Engine

[tabokie]

We need a ctl tool to do data administration work mentioned in #99.

Some subcommands I have in mind:

• Dump: dump out all operations in log files
  • ctl dump --file /path/to/file [--raft id1,id2,id3]
  • ctl dump --path /path path [--raft id1,id2,id3]
• Consistency check: check log files for logical errors
  • ctl check --path /path
• Truncate: unsafely truncate log entries in log files
  • ctl truncate --path /path --mode front/back/all --queue append/rewrite/all [--raft id1,id2,id3]
• Autofill: repair log entry holes by fill in empty message
  • ctl autofill --path /path --queue append/rewrite/all [--raft id1,id2,id3]\

We can use structopt to build a skeleton for this tool, fill in implementation later.

[yuqi1129]

/assign

[tabokie]

Closing this, the implementation of commands can be tracked in #99

[yuqi1129]

@tabokie ， Should we do not need to implement the subcommand autofill , I have noticed that you have deleted this logic in main.rs in ctl

raft-engine/ctl/src/main.rs

Lines 82 to 89 in e32e3e7

	Cmd::Dump { path, raft_groups } => self.dump(path, raft_groups),
	Cmd::Truncate {
	path,
	mode,
	queue,
	raft_groups,
	} => self.truncate(path, mode, queue, raft_groups),
	Cmd::Check { path } => self.check(path),

[tabokie]

@yuqi1129 Yes, no need