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.

* 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

Co-authored-by: Ross McFarland <ross@github.com>

Signed-off-by: Marc 'risson' Schmitt <marc.schmitt@risson.space>

aliases zones in the target zone configuration

This reverts commit b926d78c5c.

It can be useful to only synchronize zones that use a certain source. For
example, in a situation where some zones use a dynamic source and others don't,
you probably want to synchronize those with a dynamic source regularly, and
only synchronize the others when a change is made.

Although we only synchronize the zones that use a given source, we still want
to synchronize all sources to avoid deleting records that would live in another
source of the zone.

This commit adds support for zones aliases. This allows to define one or
multiple zone as aliases of an existing zone without using workarounds
like simlinks and miltiple "zones" entries in the configuration file.

An alias zone is share all of its content with it parent zone, only the
name of the zone is different.

```
zones:
  example.com.:
    aliases:
      - example.net.
      - example.org.
    sources:
      - in
    targets:
      - out
```

Known issues:
- No documentation,
- Only the `octodns-sync` and `octodns-validate` commands supports
aliases zones at this time,

I added a loop in the manager init function which convert all alias
zone to "real" ones during config validation, however I'm not sure
this is the right approach. Comments welcome.