This confirms that in addition to the recently added support for dotted
subdomains that subdomains that are not dotted are supported.  From
RFC1034 Section 3.5 this would be a <subdomain> that contains a single
<label> without <subdomain> recurring.

The is not a zone between delegated.subzone.unit.tests. and unit.tests.,
however we get a delegated subzone error.  This modifies the tests to
succeed with the added record, however the tests fail as it incorrectly
throws the managed subzone error.

Change the name of delegated.subzone, and the tests will pass cleanly.

This will result in less churn in tests for root NS support and allow us
to enable/disable things easily as needed.

This reverts commit f1fd63205e.

* Zone object no longer treats them special, some tests needed adjusting
  b/c of this, some provider's tests may also need adjusting, though
  they should not plan changes since they won't (yet) have
  SUPPORTS_ROOT_NS
* _process_desired_zone filters and warns when not supported
* YamlProvider supports them
* TinyDnsBaseSource supports them