autopkgtest should test the system installed version of the library

--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -18,7 +18,7 @@
 require 'azure/core/http/http_error'
 require 'azure/core/http/http_response'
 $LOAD_PATH.unshift(File.expand_path '../lib', __dir__)
-require File.expand_path '../lib/fog/azurerm', __dir__
+require 'fog/azurerm'
 require File.expand_path './api_stub', __dir__
 
 def storage_account_credentials