Use a longer connection timeout in pg_isready test.

Buildfarm members skink and sungazer have both recently failed this
test, with symptoms indicating that the default 3-second timeout
isn't quite enough for those very slow systems.  There's no reason
to be miserly with this timeout, so boost it to 60 seconds.

Back-patch to all versions containing this test.  That may be overkill,
because the failure has only been observed in the v10 branch, but
I don't feel like having to revisit this later.

src/bin/scripts/t/080_pg_isready.pl

@@ -15,4 +15,5 @@ my $node = get_new_node('main');
 $node->init;
 $node->start;
 
-$node->command_ok(['pg_isready'], 'succeeds with server running');
+# use a long timeout for the benefit of very slow buildfarm machines
+$node->command_ok([qw(pg_isready --timeout=60)], 'succeeds with server running');