Clarify conditions and impact of deleting a domain

Deleting a domain will delete all the objects owned by it.  This patch
updates the api documentation to clarify this and to specifiy that
a domain must first be disabled before it can be deleted

Documenation to go with fix for Bug #1097995

Change-Id: Ia5fb068ae4110b4401a7daa82ca176db1e63482a