bats test: move the logic of generating dockerfile into common lib

[yqleng1987]

Passed in local machine

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Details

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Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

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• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1516 (29925bf) into master (55a999b) will increase coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1516      +/-   ##
==========================================
+ Coverage   62.72%   62.73%   +0.01%     
==========================================
  Files         129      129              
  Lines       44158    44158              
  Branches    44158    44158              
==========================================
+ Hits        27697    27702       +5     
+ Misses      15092    15088       -4     
+ Partials     1369     1368       -1     

see 3 files with indirect coverage changes

[adamqqqplay]

LGTM, thanks!