don't define attribute methods for models without a table
don't define attribute methods for models without a table

it may be the case that there exists a model, but the table won't be created
if the database can't support it

Change-Id: I35ec6c14754e989f357873ee7e4d099d5d9bf968
Reviewed-on: https://gerrit.instructure.com/71188
Reviewed-by: James Williams  <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

instructure/switchman,instructure/switchman