Match ec2-bundle-vol on web to code

Issue #248 contained a PR which changes the way bundle_vol_command is
used by default. This change to the defaults was not reflected on the
website, so I encountered the same issue when making changes to the
bundle_vol_command in my config.
Merge pull request #646 from jtopper/bundle_vol_command_website

website: Match default ec2-bundle-vol documented on the website to the one that's used by the code.