Refactor the gravatar email changes to use webmock stubbing

The main reason for doing this is to make the tests easier to read,
rather than having to look up both the gravatar fixture, and then
correlate that with the users fixture. Putting the expected response
code in the tests is much more explicit.

test/test_helper.rb

@@ -168,5 +168,11 @@ module ActiveSupport
 
       yield
     end
+
+    def stub_gravatar_request(email, status = 200, body = nil)
+      hash = Digest::MD5.hexdigest(email.downcase)
+      url = "https://www.gravatar.com/avatar/#{hash}?d=404"
+      stub_request(:get, url).and_return(:status => status, :body => body)
+    end
   end
 end