OC-11245 Refactor the EC2 integration test code

PBI details: https://tickets.corp.opscode.com/browse/OC-11245
Jenkins job details: http://ci.opscode.us/job/knife-ec2-integration-tests/

*Depends on https://github.com/opscode/knife-cloud/pull/58 for knife-cloud changes

@adamedx @muktaa @kaustubh-d