Lock `cacerts` to `2014.08.20`

The latest version (2014.09.03) causes `berks vendor` commands to fail with:

  /opt/supermarket/embedded/lib/ruby/2.1.0/net/http.rb:920:in `connect': SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate
Switch back to `berks vendor` now that `cacerts` is locked
Update Omnibus config with sane defaults

* Use S3 caching
* Enable build retries
* Bump fetcher timeout
Create `env` before attempting to use it
Move integration test deps to cookbook’s `Gemfile`
Merge pull request #2 from opscode/schisamo/pipeline-tweaks

Fixes