Fix warning: instance variable not initialized

Initialize the variables to avoid the warning.

Addresses the following warnings:

lib/google/api_client/auth/storage.rb:51: warning: instance variable @authorization not initialized
lib/google/api_client/batch.rb:128: warning: instance variable @global_callback not initialized

lib/google/api_client/auth/storage.rb

@@ -38,6 +38,7 @@ module Google
       # @params [Object] Storage object
       def initialize(store)
         @store= store
+        @authorization = nil
       end
 
       ##