OC-11247 Cleanup script for deleting resources created in EC2 integration testing

Added cleanup script to delete servers created during ec2 integration tests run.
PBI details: https://tickets.corp.opscode.com/browse/OC-11247
Jenkins Job details: http://ci.opscode.us/job/knife-ec2-integration-tests-cleanup-resources/configure
^@adamedx @muktaa @kaustubh-d