Be picky setting the primary (originator) query as a Query parameter.

`\Cake\ORM\Query::$_query = true` only for the primary query, every other
query originated from that one will have the value set to `false`.

`Query::primary()` will return the query `_primary` value.
`Query::primary(true)` will mark the query as being the primary.
`Query::primary(false)` will mark the query as being a byproduct.