IMPROVE integration tests so they all output a diff image when multiple fail

[ndelangen]

Issue: -no all diff images are saved when screenshots do not match-

What I did

I reworked the tests a bit so they re-use the same puppeteer page and both save diff file.

[codecov]

Codecov Report

Merging #2197 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2197   +/-   ##
=======================================
  Coverage   21.43%   21.43%           
=======================================
  Files         263      263           
  Lines        5803     5803           
  Branches      700      687   -13     
=======================================
  Hits         1244     1244           
- Misses       4018     4037   +19     
+ Partials      541      522   -19

Impacted Files	Coverage Δ
app/vue/src/server/config/babel.js	0% <0%> (-100%)	⬇️
app/vue/src/server/babel_config.js	0% <0%> (-77.42%)	⬇️
...res__/update-addon-info/update-addon-info.input.js	0% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-build.js	0% <0%> (ø)	⬆️
lib/ui/src/modules/ui/configs/handle_routing.js	28.04% <0%> (ø)	⬆️
lib/codemod/src/transforms/update-addon-info.js	49.01% <0%> (ø)	⬆️
addons/info/src/components/Props.js	36.36% <0%> (ø)	⬆️
addons/info/src/components/Node.js	39.7% <0%> (ø)	⬆️
app/react/src/client/preview/element_check.js	41.17% <0%> (ø)	⬆️
app/react-native/src/bin/storybook-start.js	0% <0%> (ø)	⬆️
... and 17 more

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