Simplifies the building and running of tests
Also exports the proper env variables so that the googletest output is
colored
ctest can use env variables for some of its options so we can for
example run
CTEST_PROGRESS_OUTPUT=1 make check
to run ctest with the --progress flag
This also makes the travis test.sh script obsolete
This travis environment contains more up-to-date versions of clang and
gcc (namely 7.0.0 and 5.4.0). This allows us to remove all the code used
to get those newer versions in trusty.
Ref: https://docs.travis-ci.com/user/reference/xenial/
Uses none of the optional dependencies. This ensures that polybar can
build without any of the supposedly optional dependencies. This would
have detected the cause of the xrm build failure before it was merged
install_xcb_xrm.sh takes advantage of the travis cache but it doesn't
actually install the libraries on the system when it finds that the
compilation has been cached.
