libtracker-sparql: Add a test case

https://bugzilla.gnome.org/show_bug.cgi?id=737023
libtracker-bus: Don't crash if query_async is cancelled

Always wait for send_query to finish. In case of any exceptions from
splice_async we can not leave it hanging.

https://bugzilla.gnome.org/show_bug.cgi?id=737023