Add environment option to upload command.

This allows us to upload cookbook bundle for different environments
such as development, staging, and production. This helps to group
different bundles for the same definition in the same directory.

The URL will follow the following format:
https://<BUCKET>.amazonaws.com/<DEFINITION NAME>/<ENVIRONMENT NAME>/<VERSION NUMBER>.tar.gz

The environment will be 'dev' by default.
Merge pull request #4 from rightscale/white_14_05_acu145082_add_environment_option

Add environment option to upload command.