Close docker provider client on container terminate

[anjmao]

If provider client is not closed it leaks goroutines.

[mdelapenya]

This LGTM and thanks for your contribution!

[codecov]

Codecov Report

Merging #358 (2d2a7cf) into master (a8ca295) will increase coverage by 0.27%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #358      +/-   ##
==========================================
+ Coverage   61.91%   62.19%   +0.27%     
==========================================
  Files          15       15              
  Lines        1011     1013       +2     
==========================================
+ Hits          626      630       +4     
+ Misses        288      286       -2     
  Partials       97       97              

Impacted Files	Coverage Δ
docker.go	65.28% <0.00%> (+0.56%)	⬆️

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[anjmao]

@mdelapenya I'm not sure about coverage report failure. It says that my changed was not covered by tests, but there are many tests which calls Terminate method.

[mdelapenya]

@mdelapenya I'm not sure about coverage report failure. It says that my changed was not covered by tests, but there are many tests which calls Terminate method.

... but probably not entering the if err != nil block. So I guess the CI build did not cause the Docker client to fail while closing :)

[gianarb]

Thanks a lot!