[TEST] Use operating system specific line ending

The line endings differ between operating systems and the existing test failed
on Windows systems. This change uses the OS specific line ending.

Closes elastic/elasticsearch#443

Original commit: elastic/x-pack-elasticsearch@a458472322

src/test/java/org/elasticsearch/shield/authc/esusers/tool/ESUsersToolTests.java

@@ -648,7 +648,7 @@ public class ESUsersToolTests extends CliToolTestCase {
         assertThat(status, is(CliTool.ExitStatus.OK));
         List<String> output = terminal.getTerminalOutput();
         assertThat(output, hasSize(1));
-        assertThat(output.get(0), equalTo("No users found\n"));
+        assertThat(output.get(0), equalTo("No users found" + System.lineSeparator()));
     }
 
     @Test