Support nested domains
Add support for nested host domains:
- Allow specifying "domains" dictionary inside domains.
- Nested domains are considered sub-sections of the parent domains, and behave accordingly regarding host requirements and forced hostnames.
- Selecting a parent domain for a run selects its children.
- A host type assigned to a parent domain will be considered included into any child domain, when it's selected.
- Allow referring to domains by slash-separated paths, in addition to names (the latter to be removed after transition), in both host types, and command-line arguments.
- Rename the "kpet domain list" command to "kpet domain tree".
Edited by Nikolai Kondrashov