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
First pass to help blobstore_client comply with rubocop
Prefer single quotes for uninterpolated string
Promote variations from rubocop that are consistent in our codebase
First pass to help bosh-dev comply with rubocop
Merge remote-tracking branch 'origin/pr/361'
Wrap spec in module Bosh::Director
Include template model in backup

* [Fixes #53924557]
Inline local variable

 * ... which referred to a let()
cleanup naming
We don't use the nginx upload module any more.

Removed in 6e2d41843b282f19b82eef7cf40e295f9d0202cb.
Add spec for service_group_state and refactor starting detection.
[fixes #54048579] Make service_group_state return failing if there are
no services.
Refactor/test friendly Ruby alternative to ci_build_stemcell.sh
Use Ruby 1.9 hash style
Move ci_build_stemcell.sh logic into ruby
Resurrect env variables needed by dev/tasks/stemcell.rake

 * BUILD_PATH
 * WORK_PATH
 * STEMCELL_VERSION
Move more logic into tested lib/
Revert change to return failing when monit returns no services.

Restore old behavior of returning running in this case.
Stub MonitApi::Client instead of object under test.