Change Travis CI builds to xenial
Default was Ubuntu 14.04 (trusty), now switch to newer version of Linux - Ubuntu 16.04 (xenial). Ubuntu 14.04 (trusty) is reaching end of life in 2019, and Travis have made some changes to their build infrastructure (here and here).
Also make sure the setup.cfg
file isn't ignored anymore.
(Still expect some event tests to fail, since this branch is still using cppTango 9.2.5)