Log intermediate pending searchers as trace instead of debug
The short circuit mechanism always needs to be wrapped with the live docs. In certain scenarios the live docs isn't passed down with acceptedDocs.
For example when a has_child is wrapped in a filtered query as query and the wrapped filter is cached.
The short circuit mechanism in that case counts down based on deleted docs, which then yields lower results than is expected.

Relates to #4306
Added random filtered query logic the to random parent query tests.
Fixed bug in ParentQuery.ChildScorer#advance(), the parent value was checked for the _uid field while the _parent should have been checked.