Don't clobber test exit code at cleanup in LDAP/Kerberors tests

If the test script die()d before running the first test, the whole test
was interpreted as SKIPped rather than failed. The PostgreSQL::Cluster
module got this right.

Backpatch to all supported versions.

Discussion: https://www.postgresql.org/message-id/fb898a70-3a88-4629-88e9-f2375020061d@iki.fi

src/test/kerberos/t/001_auth.pl

@@ -188,7 +188,12 @@ system_or_bail $krb5kdc, '-P', $kdc_pidfile;
 
 END
 {
-	kill 'INT', `cat $kdc_pidfile` if -f $kdc_pidfile;
+	# take care not to change the script's exit value
+	my $exit_code = $?;
+
+	kill 'INT', `cat $kdc_pidfile` if defined($kdc_pidfile) && -f $kdc_pidfile;
+
+	$? = $exit_code;
 }
 
 note "setting up PostgreSQL instance";

src/test/ldap/t/001_auth.pl

@@ -150,7 +150,12 @@ system_or_bail $slapd, '-f', $slapd_conf,'-s0', '-h', "$ldap_url $ldaps_url";
 
 END
 {
+	# take care not to change the script's exit value
+	my $exit_code = $?;
+
 	kill 'INT', `cat $slapd_pidfile` if -f $slapd_pidfile;
+
+	$? = $exit_code;
 }
 
 append_to_file($ldap_pwfile, $ldap_rootpw);