Enable fast finishing on Travis CI

[johnbillion]

With fast finishing enabled, Travis CI will mark your build as finished as soon as one of two conditions are met: The only remaining jobs are allowed to fail, or a job has already failed.

This reduces the time it takes to receive feedback in the #core Slack channel for broken, failing, and newly fixed builds.

Ref: ​https://blog.travis-ci.com/2013-11-27-fast-finishing-builds/

[netweb]

Previously in [35150] fast_finish: true was removed as it was not working correctly and caused multiple Slack notifications, I reported it upstream in ​https://github.com/travis-ci/travis-ci/issues/4928#issue-111147790

The above issue I created was closed as a dupe of ​https://github.com/travis-ci/travis-ci/issues/1696, this issue has since been fixed", so have at it I say @johnbillion

[johnbillion]

Interestingly that Travis issue was fixed but several users have been reporting problems since then, most recently in September.

Let's add fast finishing to trunk, then we can backport if we don't see any problems.

[johnbillion]

In 45004:

Build/Test tools: Reinstate fast finishing on Travis CI.

This allows for speedier feedback for breaking changes and ongoing failures.

See #46634

[jorbin]

Going to call this fixed and close it barring a reason to do otherwise.