Test:Check if multiple Activation keys can be attached to a system

- added a function `fetch_associated_content_host` to fetch the associated content-host  from selected activation-key
- updated top menu locator names
Actually there is another way to create VM with context manager and I'm using above format as per test demand. Also 'server_name' statement is separate from vm statements.. So I think for now its okay to use above two statements separately.