pgsql: Suppress occasional failures in brin regression test.

Suppress occasional failures in brin regression test.

brin.sql included a call of brin_summarize_new_values(), and expected
it to always report exactly 5 summarization events. This failed sometimes
during parallel regression tests, as a consequence of the database-wide
VACUUM in gist.sql getting there first. The most future-proof way
to avoid variation in the test results is to forget about using
brin_summarize_new_values() and just do a plain "VACUUM brintest",
which will exercise the same code anyway.

Having done that, there's no need for preventing autovacuum on brintest;
doing so just reduces the scope of test coverage, so let's not.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/1f303fd1be51f26553e7c95d8696aa4e28ece1c6

Modified Files
--------------
src/test/regress/expected/brin.out | 9 ++-------
src/test/regress/sql/brin.sql | 4 ++--
2 files changed, 4 insertions(+), 9 deletions(-)