Currently, if a document has a parent but no layering actions,
the document immediately inherents its parents' data, which is a
bug. Instead, the child document should only layer with its
parent's data and then update its own data if it has at least
one layering action.
In addition, the base_schema.yaml under `deckhand.schemas`
has been updated to require that actions be required and
contain at least 1 layering action when parentSelector
is provided and that parentSelector be required when
actions is provided and that at least one key-value
pair be provided. (Empty actions array or empty
parentSelector object is meaningless and should be
disallowed/discouraged.)
This means that actions and parentSelector must always
both be provided (though providing neither is also
legal because layering is optional).
Unit tests have been added to verify the schema updates.
Change-Id: I77d54e2b216efc54b466f94d82ee8d36ca169c26
5c411dd05b