shared_preload_libraries = 'pg_stat_statements' failing with installcheck (compute_query_id = auto)

Hi all,
(Added Bruce and Julien in CC)

While testing installcheck with various server configurations to see
how the main regression test suites could break, I found that loading
pg_stat_statements into the backend is enough to break installcheck
as compute_query_id = auto, the default, lets the decision to compute
query IDs to pg_stat_statements itself. In short, loading
pg_stat_statements breaks EXPLAIN outputs of any SQL-based regression
test.

Running installcheck on existing installations is a popular sanity
check, as much as is enabling pg_stat_statements by default, so it
seems to me that we'd better disable compute_query_id by default in
the databases created for the sake of the regression tests, enabling
it only in places where it is relevant. We do that in explain.sql for
a test with compute_query_id, but pg_stat_statements does not do
that.

I'd like to suggest a fix for that, by tweaking the tests of
pg_stat_statements to use compute_query_id = auto, so as we would
still stress the code paths where the module takes the decision to
compute query IDs, while the default regression databases would
disable it. Please note that this also fixes the case of any
out-of-core modules that have EXPLAIN cases.

The attached is enough to pass installcheck-world, on an instance
where pg_stat_statements is loaded.

Thoughts?
--
Michael