Configurable cluster-domain name

[akhileshthipparthi]

Is this a request for help?:

Request

Is this an ISSUE or FEATURE REQUEST? (choose one):

Feature

What version of acs-engine?:

1.9.2

Orchestrator and version (e.g. Kubernetes, DC/OS, Swarm)
1.9.2

What happened:

It would be better if the cluster-domain feature is configurable via the cluster-definition file instead. This will help users who like to use custom domains .

What you expected to happen:

Make the --cluster-domain variable configurable via cluster-def file. With a Recent PR the issue related to custom DNS service IP override from cluster-def was resolved.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know:

[akhileshthipparthi]

Thank you !!