pgsql: Add PGXS options to control TAP and isolation tests

Add PGXS options to control TAP and isolation tests

The following options are added for extensions:
- TAP_TESTS, to allow an extention to run TAP tests which are the ones
present in t/*.pl.  A subset of tests can always be run with the
existing PROVE_TESTS for developers.
- ISOLATION, to define a list of isolation tests.
- ISOLATION_OPTS, to pass custom options to isolation_tester.

A couple of custom Makefile targets have been accumulated across the
tree to cover the lack of facility in PGXS for a couple of releases when
using those test suites, which are all now replaced with the new flags,
without reducing the test coverage.  This also fixes an issue with
contrib/bloom/, which had a custom target to trigger its TAP tests of
its own not part of the main check runs.

Author: Michael Paquier
Reviewed-by: Adam Berlin, Álvaro Herrera, Tom Lane, Nikolay Shaplov,
Arthur Zakirov
Discussion: https://postgr.es/m/20180906014849.GG2726@paquier.xyz

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/03faa4a8ddf04334850bf9631f305bda7a02f260

Modified Files
--------------
contrib/bloom/Makefile                     |  4 +-
contrib/oid2name/Makefile                  | 10 +----
contrib/test_decoding/Makefile             | 67 ++++++++----------------------
contrib/vacuumlo/Makefile                  | 10 +----
doc/src/sgml/extend.sgml                   | 61 ++++++++++++++++++++++++++-
src/makefiles/pgxs.mk                      | 32 +++++++++++++-
src/test/modules/brin/.gitignore           |  2 +-
src/test/modules/brin/Makefile             | 25 ++---------
src/test/modules/commit_ts/Makefile        |  6 +--
src/test/modules/snapshot_too_old/Makefile | 35 ++++------------
src/test/modules/test_pg_dump/Makefile     |  6 +--
11 files changed, 125 insertions(+), 133 deletions(-)