chore: retry certain steps on TravisCI to get more stable builds

[PK1A]

While I'm still looking into ways of getting more stable Sauce tests
there is one simple trick that we can do to increase our chances
of getting stable builds, see:
http://blog.travis-ci.com/2013-05-20-network-timeouts-build-retries/

Of course this is more of a work-around than a proper solution
but I'm afraid that we might need tricks like this one given the
number of different network-connected machines involved in the
build process. This seems to be a conclusion from the Travis-CI guys
as well...

[coveralls]

Coverage remained the same when pulling ebbfec1 on PK1A:travis_retry into 2f408ba on ariatemplates:master.

[marclaval]

👍