Add query filter tests

These tests are node specific only because we don't have other query
types implemented yet, but what they actually test is the various
filter types.

The tests are trying to cover most filter functionality; missing for
now is proper checking for ContainsFilter and TrueFilter, the rest
should be more or less covered.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>