make oauth "remember me" work when logging in on a different shard

fixes CNVS-10966

test plan:
1. create a user
2. add the user to another shard
3. log in to that shard (domain) via oauth (using an app that uses canvas
   for identity, i.e. scopes=/auth/userinfo)
4. check the "Remember my authorization" box
5. log out
6. log in again
7. you should not get prompted to reauthorize the app

Change-Id: I6045bbbf69dab46010232d96e09cf284918f14b4
Reviewed-on: https://gerrit.instructure.com/29625
Reviewed-by: Dan Dorman <ddorman@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Marc LeGendre <marc@instructure.com>
QA-Review: Marc LeGendre <marc@instructure.com>

Author: jenseng

lib/canvas/oauth/token.rb

@@ -65,8 +65,10 @@ def as_json(options={})
     end
 
     def self.find_userinfo_access_token(user, developer_key, scopes, purpose)
-      user.access_tokens.active.where(:remember_access => true, :developer_key_id => developer_key, :purpose => purpose).detect do |token|
-        token.scoped_to?(scopes) && token.scoped_to?(['userinfo'])
+      user.shard.activate do
+        user.access_tokens.active.where(:remember_access => true, :developer_key_id => developer_key, :purpose => purpose).detect do |token|
+          token.scoped_to?(scopes) && token.scoped_to?(['userinfo'])
+        end
       end
     end