Add the testing for docker package

[hwchiu]

• Add the testing for docker
• You should install the docker in your local environment
• Pull out the client out of the docker package

[codecov]

Codecov Report

Merging #18 into master will increase coverage by 5.36%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
+ Coverage   79.67%   85.03%   +5.36%     
==========================================
  Files           5        5              
  Lines         123      127       +4     
==========================================
+ Hits           98      108      +10     
+ Misses         18       12       -6     
  Partials        7        7

Impacted Files	Coverage Δ
docker/docker.go	75% <83.33%> (+58.33%)	⬆️

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[c9s]

I think you can use composition:

type Client struct {
    dockercli.Client
    Context *context.Context
}