CDAP-1078: Deprecate security.auth.server.address.

Instead of just changing the property, the old property is deprecated and linked to the new property that replaces it.

Fixes [CDAP-1078](https://issues.cask.co/browse/CDAP-1078)

Staged at [web-server](http://stg-web101.sw.joyent.continuuity.net/cdap/2.7.0-SNAPSHOT-2.7.0_doc_fixes/en/admin-manual/installation/security.html)