Adding a descriptive auth error message. (firebase#1774)

* Add a descriptive error message. * Addressing rayo's comments.

Author: ankitaj224

firebase-installations/src/main/java/com/google/firebase/installations/FirebaseInstallations.java

@@ -109,6 +109,11 @@ public Thread newThread(Runnable r) {
  + "with Firebase server APIs: It identifies your application with Firebase."
  + "Please refer to https://firebase.google.com/support/privacy/init-options.";
 
+ private static final String AUTH_ERROR_MSG =
+ "Installation ID could not be validated with the Firebase servers (maybe it was deleted). "
+ + "Firebase Installations will need to create a new Installation ID and auth token. "
+ + "Please retry your last request.";
+
  /** package private constructor. */
  FirebaseInstallations(
  FirebaseApp firebaseApp,
@@ -378,7 +383,7 @@ private void doNetworkCallIfNecessary(boolean forceRefresh) {
  } else if (prefs.isNotGenerated()) {
  // If there is no fid it means the call failed with an auth error. Simulate an
  // IOException so that the caller knows to try again.
- triggerOnException(prefs, new IOException("cleared fid due to auth error"));
+ triggerOnException(prefs, new IOException(AUTH_ERROR_MSG));
  } else {
  triggerOnStateReached(prefs);
  }