Adding cleanup_repo task to cleanup existing repos in the node

Since this task cleans up existing repos in the node, contrail_install_repo created by setup.sh would be the only
enabled repo in the node. This will help make sure all packages are installed from contrail_install_repo

Change-Id: Ie46ed4e85fdfc40ac872b5ff070f3e0091a7ebf4
Merge "Adding cleanup_repo task to cleanup existing repos in the node"