Implement new abstract MappedLoginService methods added in Jetty 9.3

Eclipse Neon comes with Jetty 9.3 which is causing unimplemented
abstract method errors in test class AppServer when using the JGit or
EGit Neon target platform. Fix this by adding dummy implementations.

Change-Id: Ie49107d814a846997de95f149e91fe1ec2fbe4d8
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.junit.http/src/org/eclipse/jgit/junit/http/AppServer.java

@@ -181,6 +181,14 @@ public class AppServer {
 			protected void loadUsers() throws IOException {
 				putUser(username, new Password(password), new String[] { role });
 			}
+
+			protected String[] loadRoleInfo(KnownUser user) {
+				return null;
+			}
+
+			protected KnownUser loadUserInfo(String usrname) {
+				return null;
+			}
 		};
 
 		ConstraintMapping cm = new ConstraintMapping();