[COOK-4576] - No way to override `AuthorizedKeysFile`

Signed-off-by: Sean OMeara <someara@opscode.com>
[COOK-4584] - Use Upstart on Ubuntu 12.04

Signed-off-by: Sean OMeara <someara@opscode.com>
[COOK-4585] - skip match block in template if empty or unset

Signed-off-by: Sean OMeara <someara@opscode.com>
[COOK-4586] OpenSSH Gentoo support

Signed-off-by: Sean OMeara <someara@opscode.com>