Display proper error message when LDAP is unavailable

At the moment the error message 'Incorrect username or password.' is
displayed when querying the LDAP server fails because it is
unavailable. This message is misleading since the user cannot make
the login succeed by correcting the username or password. With this
change now a proper error message is displayed so that the user can
understand that login is not possible due to the LDAP server not
being available.

Change-Id: I4afa503642537dbdb33c1031220281f923dddfc8
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-common/src/main/java/com/google/gerrit/common/auth/userpass/LoginResult.java

@@ -14,7 +14,40 @@
 
 package com.google.gerrit.common.auth.userpass;
 
+import com.google.gerrit.reviewdb.AuthType;
+
 public class LoginResult {
   public boolean success;
   public boolean isNew;
+
+  protected AuthType authType;
+  protected Error error;
+
+  protected LoginResult() {
+  }
+
+  public LoginResult(final AuthType authType) {
+    this.authType = authType;
+  }
+
+  public AuthType getAuthType() {
+    return authType;
+  }
+
+  public void setError(final Error error) {
+    this.error = error;
+    success = error == null;
+  }
+
+  public Error getError() {
+    return error;
+  }
+
+  public static enum Error {
+    /** Username or password are invalid */
+    INVALID_LOGIN,
+
+    /** The authentication server is unavailable or the query to it timed out */
+    AUTHENTICATION_UNAVAILABLE
+  }
 }