[ftr/percy] integrate percy with functional test runner

[spalger]

Testing out integrating Percy with the functional test runner: https://percy.io/Elastic/kibana-ftr

[liza-mae]

@spalger can we make an official PR for this functionality?

• We don't need to include the test snapshots on each test right now, we will do that separately.
• We should wrap py.snapshot() also so the tests don't call it specially.
• We won't be enabling on CI on PR just yet.
• Keep the infra part, below files?
  https://github.com/elastic/kibana/pull/32953/files#diff-e4403a877d80de653400d88d85e4801a
  https://github.com/elastic/kibana/pull/32953/files#diff-b9cfc7f2cdf78a7f4b91a753d10865a2
  https://github.com/elastic/kibana/pull/32953/files#diff-a916d280958266daaec2da07dd24a2c6
  https://github.com/elastic/kibana/pull/32953/files#diff-94eadb18855f7c061f27db05309db9fc
  https://github.com/elastic/kibana/pull/32953/files#diff-f01777476a7ddc5e194adc66c0be4335
  https://github.com/elastic/kibana/pull/32953/files#diff-3878257169be4a8785442e19f0b2e776
  https://github.com/elastic/kibana/pull/32953/files?file-filters%5B%5D=.js&file-filters%5B%5D=.lock&file-filters%5B%5D=.sh&file-filters%5B%5D=.ts#diff-7fe9f1bbad66ba9f1d82dbeee5c935e7
  https://github.com/elastic/kibana/pull/32953/files?file-filters%5B%5D=.js&file-filters%5B%5D=.lock&file-filters%5B%5D=.sh&file-filters%5B%5D=.ts#diff-ae274aea0adcd434106aa222b8b3933f
  https://github.com/elastic/kibana/pull/32953/files?file-filters%5B%5D=.js&file-filters%5B%5D=.lock&file-filters%5B%5D=.sh&file-filters%5B%5D=.ts#diff-4e97366b846ecd956c4a4c221f8988f2
  https://github.com/elastic/kibana/pull/32953/files?file-filters%5B%5D=.js&file-filters%5B%5D=.lock&file-filters%5B%5D=.sh#diff-f0e2712ea70db1ef300c77987f5aa706
  https://github.com/elastic/kibana/pull/32953/files?file-filters%5B%5D=.lock&file-filters%5B%5D=.sh#diff-23025c69dccfb5ed50c507d88068f1c6
  https://github.com/elastic/kibana/pull/32953/files?file-filters%5B%5D=.lock&file-filters%5B%5D=.sh#diff-682926488e87c3529b3c0ae0081a91d9

[spalger]

Okay, it seems the flakiness might have actually just been coincidental... Going to give it a couple more goes.

[liza-mae]

Thanks @spalger it is looking better.

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[liza-mae]

Nice @spalger! Those changes look promising at fixing the chromium download failures.

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[liza-mae]

@spalger can we please look to get this PR updated and merged or would you like me to merge my PR off of your PR? Please let me know.

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