Add API to get Auth Token Type used by authenticator.

When using different auth protocols e.g. ClientLogin and
OAuth2 it is important to know the type of the token in order
to construct "Authorization" header. Currently we have to
store auth token vaue/auth token type association elsewhere
which makes it a subject for errors.

Change-Id: I3b8c05672f5394ad806f257c9f6bb378ebf990d7
diff --git a/src/main/java/com/android/volley/toolbox/AndroidAuthenticator.java b/src/main/java/com/android/volley/toolbox/AndroidAuthenticator.java
index bdf7091..18f8597 100644
--- a/src/main/java/com/android/volley/toolbox/AndroidAuthenticator.java
+++ b/src/main/java/com/android/volley/toolbox/AndroidAuthenticator.java
@@ -73,6 +73,13 @@
         return mAccount;
     }
 
+    /**
+     * Returns the Auth Token Type used by this authenticator.
+     */
+    public String getAuthTokenType() {
+        return mAuthTokenType;
+    }
+
     // TODO: Figure out what to do about notifyAuthFailure
     @SuppressWarnings("deprecation")
     @Override