Adding a descriptive auth error message. (#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);
     }