Tests for NodeGroup query

This adds tests similar to those used for node query. For now the
prop_queryGroup_noUnknown is disabled and commented out, as it is
fasifiable with ndparams and ipolicy. It may be removed or fixed
later on.

Also, prop_queryGrooup_types has one less property checked - it is
not the case that number of result rows should be equal to number
of nodes.

Signed-off-by: Agata Murawska <agatamurawska@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>