Change error message when bookshelf db connection fails at start

[petersg83]

fix #4589

[codecov]

Codecov Report

Merging #5499 into master will increase coverage by 0.00%.
The diff coverage is 20.00%.

@@           Coverage Diff           @@
##           master    #5499   +/-   ##
=======================================
  Coverage   17.73%   17.73%           
=======================================
  Files         687      687           
  Lines       10151    10154    +3     
  Branches     1643     1644    +1     
=======================================
+ Hits         1800     1801    +1     
- Misses       6961     6962    +1     
- Partials     1390     1391    +1     

Flag	Coverage Δ
#front	13.15% <20.00%> (+<0.01%)	⬆️
#unit	37.04% <ø> (ø)

Impacted Files	Coverage Δ
...s/strapi-admin/admin/src/containers/App/reducer.js	60.00% <20.00%> (-3.64%)	⬇️

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[alexandrebodin]

LGTM, Nice job