Fix attachment_fu (zendesk) for rails console on dbadmin

https://zendesk.atlassian.net/browse/INFR-764

*Problem*

When a user runs rails console, it may create the attachment-fu temporary directory as that user. When the same happens for other users the directory creation will fail due to lack of permissions.

*Solution*

When the rails console creates the directory as a user, make sure it has perms for other users to write to it.

*Risks*

We limit this action to user-run processes, so it won't take affect on the app servers.


Code Review @osheroff @marcosvm @grosser 

cc @pdeuter @bsandvik