Add support for platform "amazon" in accordance to my agreement with treasure-data/chef-td-agent current
maintainer, repeatedly@gmail.com.  As per issue, Uneccesarly strick platform check #18,
  "We don't have a test environment for Amazon Linux and we don't guarantee td-agent works on Amazon Linux.
  If it is OK, please send a PR :)"
Done.

thanks!
Merge pull request #21 from benself/master

Add support for platform "amazon" (tested)