bool query: parser should return match_all in case there are no clauses

This also fixes has_parent filters with a nested empty bool filter
(see test SimpleChildQuerySearchTests#test6722, the test should actually expect
either 0 results when searching for has_parent "test" or one result when
search for has_parent "foo")

closes #7240
Seems like test data like this can just be inlined in the test case?  I would do that for most of these actually, just my opinion (it seems a little weird to me to have test data pulled in as resources for such small data).