CA-146592:  Change default search when in Infrastructure view

- If XenCenter node or a  disconnected host is selected, show the default search.
- Otherwise, find the top-level parent (= pool or standalone server) and show the search restricted to that.
- In the case of multiselect, if all the selections are within one pool (or standalone server), then show that report.
- Otherwise show everything, as on the XenCenter node.

Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>