Allow support for host plugins of CoreDNS

1. Proposed title of this feature request
    - Want to add host entries in /etc/host of CoreOS node 
2. What is the nature and description of the request?
    - Allowing customized setting in CoreDNS in order to fit the business environment.
      Available to edit the config-map of CoreDNS operator (e.g. apply "hosts plugin") without            force rollback.
      https://coredns.io/plugins/hosts/

3. Why does the customer need this? (List the business requirements here)
    - Customer wanted to use host plugins of coredns so that he can define some entries in               CoreOS's /etc/hosts.

4. List any affected packages or components.
       DNS operator