Make get_test_unconnected_page more robust

Travis tests are regularly 'red' due to bug 67956.  This
changeset should reduce the frequency of this problem by
fetching Talk: pages which should be valid for wikibase
items, but also check 10 of them and return the first
without a wikibase item.

Change-Id: I8df00fb9d492e0d400360031c6088bf4a2f2cf4a
Merge "Make get_test_unconnected_page more robust"