Fail fast (#1578)

If any of the commands in the build script fail we don't want
to continue.

Travis should really provide and option for this and it should
probably be the default:
  travis-ci/travis-ci#1066

Author: sbc100

.travis.yml

@@ -33,6 +33,7 @@ jobs:
       before_script:
         - ./check.py --test-waterfall --only-prepare
       script:
+        - set -o errexit
         - flake8
         - BUILD_SUBDIR=${BUILD_SUBDIR:-.}
         - mkdir -p ${BUILD_SUBDIR} && cd ${BUILD_SUBDIR}