Use built image first when lain build

[ccl0326]

as title.

[codecov]

Codecov Report

Merging #48 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master     #48      +/-   ##
=========================================
- Coverage    4.53%   4.52%   -0.02%     
=========================================
  Files          33      33              
  Lines        1608    1615       +7     
=========================================
  Hits           73      73              
- Misses       1535    1542       +7

Impacted Files	Coverage Δ
lain_cli/build.py	0% <0%> (ø)	⬆️

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