Blueprint for a subsite should not need a superfluous hst:site node

A blueprint for a subsite still needs an hst:site node in its configuration, otherwise channels created from this blueprint won't have hst:sites in their HST configuation. These hst:site nodes could be generated by convention instead.

For example, imagine a blueprint 'my-subsite' with two configuration nodes: hst:channel (for the channel information) and hst:configuration (for the subsite-specific HST configuration). The bootstrap content tree for this subsite is located at /hippo:configuration/hippo:queries/hippo:templates/new-subsite/hippostd:templates/my-subsite.

Such a configuration actually won't work right now: when a new subsite 'test' is created from this blueprint, the necessary 'hst:site' nodes under /hst:hst/hst:sites (/hst:hst/hst:sites/test-live and /hst:hst/hst:sites/test-preview) won't be created. The channel manager only creates these hst:site nodes when an hst:site node is present in the blueprint. That hst:site node must contain a hst:content child node whose docbase property points to an arbitrary location. That location will be overwritten by the location of the copied bootstrap content of the blueprint.

Instead of having such a superfluous hst:site node in the blueprint, the channel manager should simply create a live and preview hst:site node with the default setup when the blueprint does not contain any hst:site node.