build: Remove clumsy syntax in Travis-CI config
build: Remove clumsy syntax in Travis-CI config

We were using a clumsy workaround in order to
get good failure information when a Travis-CI build
failed and also to make it stop at the point of
failure.

This commit uses some techniques to workaround
travis-ci/travis-ci#1066, which asserts that
a Travis-CI job should stop when a before_install
or script command fails.  Today, Travis-CI
continues with the next commands.

This was tested with both an intentional build
script error and a compilation error.  In both
cases the Travis-CI job ended at the point of
failure and the logs were clear enough to
diagnose the problem.

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers