In pg_rewind test suite, triple promote timeout to 90s.

Thirty seconds was not consistently enough for promotion to complete on
buildfarm members sungazer and tern.  Experiments suggest 43s would have
been enough.  Back-patch to 9.5, where pg_rewind was introduced.

src/test/perl/PostgresNode.pm

@@ -404,7 +404,7 @@ sub poll_query_until
 {
 	my ($self, $dbname, $query) = @_;
 
-	my $max_attempts = 30;
+	my $max_attempts = 90;
 	my $attempts     = 0;
 	my ($stdout, $stderr);
 
@@ -426,7 +426,7 @@ sub poll_query_until
 		$attempts++;
 	}
 
-	# The query result didn't change in 30 seconds. Give up. Print the stderr
+	# The query result didn't change in 90 seconds. Give up. Print the stderr
 	# from the last attempt, hopefully that's useful for debugging.
 	diag $stderr;
 	return 0;