Fix missing 'TRAVIS_REPO_SLUG=travis-ci/travis-ci'
Export the 'build home directory' as environment variable
Use $HOME instead of '/home/travis'
Expect that all TRAVIS env-vars are exported with a value
Rename the variable and export with double quotes
Use Travis::Build::BUILD_DIR instead of hard-coded value
Remove examples/build_script.sh since no more generated
Remove 'fileutils' dependency
Change to new behaviour of 'env' should matcher

Before, the matcher checked the definition of the environment variable
BEFORE the `export VAR=...` call. Now the spec matcher consider the
exported value.
Cosmetic change