Enable a admin to configure a global search domain. That is, if a
subnet is not created with a search domain (commit
d9f3ee826acf3fc5a1c436361790940237ef9784) then is a domain is
defined in the configuration file then we can use that one.
In the nsxv section there will be a new variable
- dns_search_domain
Change-Id: I112a00dbc89b1c7702e82ecfa6ec974b7b9cce8d