Fix pd-ctl help output

[lhy1024]

What problem does this PR solve?

Repair help output format.

Before:

# ./pd-ctl --help
Usage of ./pd-ctl:
      --cacert string   path of file that contains list of trusted SSL CAs.
      --cert string     path of file that contains X509 certificate in PEM format.
  -d, --detach          Run pdctl without readline (default true)
  -i, --interact        Run pdctl with readline
      --key string      path of file that contains X509 key in PEM format.
  -u, --pd string       The pd address (default "http://127.0.0.1:2379")
  -V, --version         print version information and exit
pflag: help requested

After:

# ./pd-ctl --help                                                                                                      
Usage of ./pd-ctl:
      --cacert string   The path of file that contains list of trusted SSL CAs.
      --cert string     The path of file that contains X509 certificate in PEM format.
  -d, --detach          Run pdctl without readline (default true).
  -h, --help            Help message.
  -i, --interact        Run pdctl with readline.
      --key string      The path of file that contains X509 key in PEM format.
  -u, --pd string       The pd address (default "http://127.0.0.1:2379").
  -V, --version         Print version information and exit.

Check List

Tests

• Unit test

[codecov-io]

Codecov Report

Merging #1763 into master will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1763      +/-   ##
==========================================
- Coverage   76.92%   76.76%   -0.16%     
==========================================
  Files         162      162              
  Lines       15893    15893              
==========================================
- Hits        12225    12201      -24     
- Misses       2646     2662      +16     
- Partials     1022     1030       +8

Impacted Files	Coverage Δ
pkg/etcdutil/etcdutil.go	72.46% <0%> (-15.95%)	⬇️
server/schedulers/shuffle_hot_region.go	58.97% <0%> (-6.42%)	⬇️
server/schedulers/random_merge.go	61.53% <0%> (-5.13%)	⬇️
server/tso/tso.go	81.65% <0%> (-3.67%)	⬇️
server/grpc_service.go	57.48% <0%> (-1.31%)	⬇️
server/server.go	82.21% <0%> (-0.58%)	⬇️
server/region_syncer/client.go	78.94% <0%> (+1.31%)	⬆️
server/member/leader.go	79.59% <0%> (+3.06%)	⬆️

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[sre-bot]

/run-all-tests