* Use one job for MacOS Homebrew builds cache with Travis workspaces

* Brew build job needs to both feed to other jobs and cache between builds

* Move Linux jobs to the Final stage

With only 1 OSX job in S1, the Linux part is now the critical path and holds the build time back

https://blog.travis-ci.com/2019-04-15-xenial-default-build-environment

Also: __sudo: required__ no longer is [Travis are now recommending removing the __sudo__ tag](https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration) because the sudo command is always available in Travis CI and there is no longer any way to turn it off.

* Add a dedicated stage to each OSX build to download/build brew packages
* Remove bottle building logic and the corresponding trace output from the project build stage

* fix built bottle & metadata cleanup when bottle is missing
* -e mode for before_cache step
* faster finish when already the latest version

This reverts commit 5288ba5f.

fix: cache