travis: Enhance travis.yml
travis: Enhance travis.yml

Simplify .travis.yml thanks to the previous changes. This allows for
more clarity in travis code and it is easier to maintain.

Signed-off-by: Sebastien Boeuf <90b401417360b1924ef3f520ddee932686110f85@intel.com>

containers/virtcontainers,containers/virtcontainers