Added option for enable ebs-optimized 

PLEASEREVIEW: @MatthaeusHarris @declanshanaghy @instantlinux  @gtrummell @rajivbattula @dpezely @hyfather

- Added option for enable ebs-optimized
- Added unit test
- Verified "ebs optimized" was enable when provision AWS instance using Vagrantfile from local machine (Not using stackmakr)


TODO:
- Discuss how to deploy new vagrant-aws for stackmakr.
- Merge to master after .conf 2013.
- Verify "ebs optimized" will be enable using stackmakr.