In PostgresNode.pm, don't pass SQL to psql on the command line

The Msys shell mangles certain patterns in its command line, so avoid
handing arbitrary SQL to psql on the command line and instead use
IPC::Run's redirection facility for stdin. This pattern is already
mostly whats used, but query_poll_until() was not doing the right thing.

Problem discovered on the buildfarm when a new TAP test failed on msys.

src/test/perl/PostgresNode.pm

@@ -2127,7 +2127,7 @@ sub poll_query_until
 
 	my $cmd = [
 		$self->installed_command('psql'),
-		'-XAt', '-c', $query, '-d', $self->connstr($dbname)
+		'-XAt', '-d', $self->connstr($dbname)
 	];
 	my ($stdout, $stderr);
 	my $max_attempts = 180 * 10;
@@ -2135,7 +2135,8 @@ sub poll_query_until
 
 	while ($attempts < $max_attempts)
 	{
-		my $result = IPC::Run::run $cmd, '>', \$stdout, '2>', \$stderr;
+		my $result = IPC::Run::run $cmd, '<', \$query,
+		  '>', \$stdout, '2>', \$stderr;
 
 		$stdout =~ s/\r\n/\n/g if $Config{osname} eq 'msys';
 		chomp($stdout);