pgsql: Add wait_for_subscription_sync for TAP tests.

Add wait_for_subscription_sync for TAP tests.

The TAP tests for logical replication in src/test/subscription are using
the following code in many places to make sure that the subscription is
synchronized with the publisher:

  $node_publisher->wait_for_catchup('tap_sub');
  $node_subscriber->poll_query_until('postgres',
    qq[SELECT count(1) = 0
       FROM pg_subscription_rel
       WHERE srsubstate NOT IN ('r', 's')]);

The new function wait_for_subscription_sync() can be used to replace the
above code. This eliminates duplicated code and makes it easier to write
future tests.

Author: Masahiko Sawada
Reviewed by: Amit Kapila, Shi yu
Discussion: https://postgr.es/m/CAD21AoC-fvAkaKHa4t1urupwL8xbAcWRePeETvshvy80f6WV1A@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0c20dd33db1607d6a85ffce24238c1e55e384b49

Modified Files
--------------
src/test/perl/PostgreSQL/Test/Cluster.pm           | 44 +++++++++++++++++++
src/test/subscription/t/001_rep_changes.pl         | 18 ++------
src/test/subscription/t/002_types.pl               |  7 +--
src/test/subscription/t/004_sync.pl                | 18 +++-----
src/test/subscription/t/005_encoding.pl            |  9 +---
src/test/subscription/t/006_rewrite.pl             |  9 +---
src/test/subscription/t/007_ddl.pl                 |  9 +---
src/test/subscription/t/008_diff_schema.pl         | 12 ++----
src/test/subscription/t/010_truncate.pl            |  8 +---
src/test/subscription/t/011_generated.pl           |  5 +--
src/test/subscription/t/013_partition.pl           | 20 +++------
src/test/subscription/t/014_binary.pl              |  5 +--
src/test/subscription/t/015_stream.pl              |  9 +---
src/test/subscription/t/016_stream_subxact.pl      |  9 +---
src/test/subscription/t/017_stream_ddl.pl          |  9 +---
.../subscription/t/018_stream_subxact_abort.pl     |  9 +---
.../subscription/t/019_stream_subxact_ddl_abort.pl |  9 +---
src/test/subscription/t/021_twophase.pl            | 18 ++------
src/test/subscription/t/023_twophase_stream.pl     | 10 +----
src/test/subscription/t/024_add_drop_pub.pl        | 18 ++------
.../subscription/t/025_rep_changes_for_schema.pl   | 18 +++-----
src/test/subscription/t/027_nosuperuser.pl         |  9 +---
src/test/subscription/t/028_row_filter.pl          | 19 ++------
src/test/subscription/t/029_on_error.pl            |  5 +--
src/test/subscription/t/030_origin.pl              | 19 ++------
src/test/subscription/t/031_column_list.pl         | 50 ++++++++--------------
src/test/subscription/t/100_bugs.pl                | 14 ++----
27 files changed, 129 insertions(+), 260 deletions(-)