Default log level to Info without hardcoding it in installer

[0rzech]

Partially solves #2984.

[codecov-io]

Codecov Report

Merging #3041 into master will decrease coverage by 0.03%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #3041      +/-   ##
==========================================
- Coverage   33.38%   33.34%   -0.04%     
==========================================
  Files         270      270              
  Lines       39570    39566       -4     
==========================================
- Hits        13209    13195      -14     
- Misses      24478    24484       +6     
- Partials     1883     1887       +4

Impacted Files	Coverage Δ
routers/install.go	0% <0%> (ø)	⬆️
modules/setting/setting.go	46.91% <100%> (-0.28%)	⬇️
models/repo_indexer.go	45.54% <0%> (-3.47%)	⬇️
models/repo.go	37.82% <0%> (-0.19%)	⬇️

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[lafriks]

LGTM

[lunny]

LGTM