Use matrix.fast_finish for the travis-ci to mark the build ASAP

Use matrix.fast_finish for the travis-ci to mark the build ASAP

AFAIR there is shortage of osx workers on travis-ci, IOW builds that
requires them can wait fair amount of time in the queue by just waiting.

Plus linux workers AFAICS can run multiple jobs in parallel (4-5), while
osx does not.

Hence if we do allow failures for osx (and right now they have a lot of
failed tests) let's mark build result based on tests under linux only.

So in a nut shell this will reduce build time from 5 hours to 20-30
minutes.