Prune Makefile by converting targets to rake tasks

Closes: #1677 (closed)

Changes

• Make no_changes a rake task.
• Mark no_changes and purge_cache as dependent tasks of build task. These are never used individually. Also, these two tasks are under prepare namespace.
• Invoke license:check and move_to_platform_dir as part of build task. In Makefile, they always followed build task
• Create wrapper tasks for releasing packages and docker iamge - release:package and release:docker - in top level Rakefile
• Create wrapper task for building package and syncing to s3 - build_and_sync - in top level Rakefile
• Create get_release_bucket method to identify the release bucket to use
• Move ohai-helper to a library method, not an executable
• See if get_release_bucket can be auto identified by checking if currently on tag or not