fix: make pouch network non-existent return exit code 1

[allencloud]

Signed-off-by: Allen Sun allensun.shl@alibaba-inc.com

Ⅰ. Describe what this PR did

In the original code, parent command of Pouch has no execution function which could be tell users error happens.

I wish to add this into integration test, however I have no idea how to check exit code in test framework.

@sunyuan3

Ⅱ. Does this pull request fix one issue?

fix #1076

Ⅲ. Describe how you did it

add a RunE function in parent command.

Ⅳ. Describe how to verify it

root@ubuntu:~/go/src/github.com/alibaba/pouch# echo $?
1
root@ubuntu:~/go/src/github.com/alibaba/pouch#
root@ubuntu:~/go/src/github.com/alibaba/pouch#
root@ubuntu:~/go/src/github.com/alibaba/pouch# ./pouch network sdfghjk dfghj
Error: command 'pouch network sdfghjk' does not exist.
Please execute `pouch network --help` for more help
root@ubuntu:~/go/src/github.com/alibaba/pouch# echo $?
1
root@ubuntu:~/go/src/github.com/alibaba/pouch# ./pouch network
Error: requires at least 1 arg(s), only received 0
root@ubuntu:~/go/src/github.com/alibaba/pouch# echo $?
1

Ⅴ. Special notes for reviews

none

[codecov-io]

Codecov Report

Merging #1089 into master will increase coverage by 0.08%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1089      +/-   ##
==========================================
+ Coverage   16.46%   16.55%   +0.08%     
==========================================
  Files         161      161              
  Lines        8896     8838      -58     
==========================================
- Hits         1465     1463       -2     
+ Misses       7327     7272      -55     
+ Partials      104      103       -1

Impacted Files	Coverage Δ
cli/volume.go	8.19% <0%> (-0.14%)	⬇️
cli/network.go	0% <0%> (ø)	⬆️
cli/cli.go	0% <0%> (ø)	⬆️
client/client.go	100% <0%> (+66.66%)	⬆️

[sunyuan3]

LGTM