Avoid and detect SIGPIPE race in TAP tests.

Don't write to stdin of a psql process that could have already exited
with an authentication failure.  Buildfarm members crake and mandrill
have failed once by doing so.  Ignore SIGPIPE in all TAP tests.
Back-patch to v10, where these tests were introduced.

Reviewed by Michael Paquier.

Discussion: https://postgr.es/m/20171209210203.GC3362632@rfd.leadboat.com

src/test/authentication/t/001_password.pl

@@ -44,8 +44,7 @@ sub test_role
 
 	$status_string = 'success' if ($expected_res eq 0);
 
-	my $res =
-	  $node->psql('postgres', 'SELECT 1', extra_params => [ '-U', $role ]);
+	my $res = $node->psql('postgres', undef, extra_params => [ '-U', $role ]);
 	is($res, $expected_res,
 		"authentication $status_string for method $method, role $role");
 }

src/test/authentication/t/002_saslprep.pl

@@ -41,8 +41,7 @@ sub test_login
 	$status_string = 'success' if ($expected_res eq 0);
 
 	$ENV{"PGPASSWORD"} = $password;
-	my $res =
-	  $node->psql('postgres', 'SELECT 1', extra_params => [ '-U', $role ]);
+	my $res = $node->psql('postgres', undef, extra_params => [ '-U', $role ]);
 	is($res, $expected_res,
 		"authentication $status_string for role $role with password $password"
 	);

src/test/perl/TestLib.pm

@@ -75,6 +75,10 @@ BEGIN
 INIT
 {
 
+	# Return EPIPE instead of killing the process with SIGPIPE.  An affected
+	# test may still fail, but it's more likely to report useful facts.
+	$SIG{PIPE} = 'IGNORE';
+
 	# Determine output directories, and create them.  The base path is the
 	# TESTDIR environment variable, which is normally set by the invoking
 	# Makefile.