fix: make pkg client independent to other inner pkgs

[allencloud]

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

Ⅰ. Describe what this PR did

We have discussed that we should make package pkg to be a very independent package which could let others to import directly.

To achieve this, I think we should make client package be a closure with no import other alibaba/pouch packages.

Currently I find that we import 3 packages:

• github.com/alibaba/pouch/pkg/utils which uses TLSConfig;
• github.com/pkg/errors which uses errors
• github.com/alibaba/pouch/api/types which could be moved to package client in the future.

This PR only make the first and second package out of client package.

Ⅱ. Does this pull request fix one issue?

none

Ⅲ. Describe how you did it

none

Ⅳ. Describe how to verify it

none

Ⅴ. Special notes for reviews

none

[codecov-io]

Codecov Report

Merging #962 into master will increase coverage by <.01%.
The diff coverage is 8.33%.

@@            Coverage Diff             @@
##           master     #962      +/-   ##
==========================================
+ Coverage   12.94%   12.95%   +<.01%     
==========================================
  Files         123      122       -1     
  Lines        8314     8308       -6     
==========================================
  Hits         1076     1076              
+ Misses       7142     7136       -6     
  Partials       96       96

Impacted Files	Coverage Δ
cli/cli.go	0% <ø> (ø)	⬆️
client/utils.go	0% <0%> (ø)	⬆️
client/client.go	11.11% <9.09%> (-22.23%)	⬇️

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[allencloud]

LGTM