Use cross-platform /dev/null file

Issue raised in this Stack Overflow question:
http://stackoverflow.com/questions/17602148/how-to-deploy-cloudfoundry-to-aws

Answer from here:
http://stackoverflow.com/a/8682009/126042
Use polymorphism instead of primitives and conditionals
Spec each infrastrcuture directly for clarity
Introduce hypervisor notion so we can use it in the stemcell filename
Inject infratrcuture object instead of primitive name
[#53976067] bosh-dev knows that openstack stemcell name includes hypervisor
ci_build.sh display sorted `env`

 * moving this out of jenkins
Add meta task to encapsulate ci:setup:rspec + unit/integration

  * move logic out of Jenkins
  * fix .gitignore for JUnit reports
sort and cleanup .gitignore
Move ci:rspec:setup into ci_build.sh

 * the JUnit xml is jenkins specific
Travis uses the same testing meta-tasks as Jenkins
ci_build_stemcell.sh prints sorted env
Travis uses '--trace' when executing rake
ci_build_stemcell.sh uses '--trace' when running rake
Enable rubocop for aws/

 * turn off encoding warning globally
Enable rubocop for bat/
Move the bundle path outside the workspace (e.g. bosh/) so that rubocop doesn't lint gems
[Fixes #53992139] Re-introduce trailing slash accidentally removed in d788172
instead of shelling out, use RuboCop's new Rake task
Disable rubocop for bat/

* merge of pr/363 exposed more errors, re-enable later