More business with $Test::Builder::Level in the TAP tests

Hi all,

Following up with Peter E's recent commit 73aa5e0 to add some
forgotten level incrementations, I got to look again at what I did
wrong and why this stuff is useful.

I have gone through all the TAP tests and any code paths using
subroutines, to note that we could improve the locations of the
reports we get by adding more $Test::Builder::Level. The context is
important, as some code paths use rather-long routines and also
argument values that allow to track easily which test path is being
taken (like pg_rewind), so there is no need to add anything in such
places. The attached patch adds incrementations for the tests where
the debugging becomes much easier if there is a failure.

Thoughts?
--
Michael