Re-add BRIN isolation test

Alvaro Herrera <alvherre@alvh.no-ip.org>

Commit: ae372e60b98990863058edc596df8a20207b08d0
Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: 2015-08-13T17:41:52Z
Releases: 9.5.0
Re-add BRIN isolation test

This time, instead of using a core isolation test, put it on its own
test module; this way it can require the pageinspect module to be
present before running.

The module's Makefile is loosely modeled after test_decoding's, so that
it's easy to add further tests for either pg_regress or isolationtester
later.

Backpatch to 9.5.

Files