004_timeline_switch TAP test may fail

Hi hackers!

I found that after commit 7185eddf0522b3146ed1ff6e063e8e129e77c706 we
got little omission
in TAP test 004_timeline_switch:
...
my $node_standby_1 = PostgreSQL::Test::Cluster->new('standby_1');
...
$node_primary->stop;

There is no guarantee that standby_1 and standby_2 was successfully
connected to primary and start
streaming before primary stopped.

 I think we must ensure that primary knows about standby_1 and standby_2

--
With best regards,
Sergey Tatarintsev,
PostgresPro