Move package-builder/util to top-level util
Major updates to the util module

- Make ConfigFile a bit smarter, and alias .update to file_update
- Allow ConfigFile.sed to run other sed commands than just replacing
- Update file_update to optionally uncomment and update a config
  option rather than simply changing it

- Include the noninteractive flag for all apt-get operations
- Make apt.add_repo a bit smarter; use add-apt-repository if
  installed, otherwise append the provided source to sources.list

- Service module methods now use either the service command, if
  available, or the corresponding init.d script
- Make rpm be a little quieter in yum.add_repo_rpm
- Add yum.enable_repo and yum.disable_repo, which uses
  yum-config-manager if available, otherwise attempts a change itself
  in a corresponding yum.repos.d file

- Change run() to sudo() in a bunch of spots where necessary
Move push_key to util.keys