Some tasks don't have to run on every tenant. The task to calculate the
TSV is only done for records which were present before we added the TSV
column, and that isn't going to happen in any tenants because we added
the TSV column before adding the tenants table. Similarly, the migration
needed for existing polls isn't necessary because there weren't any
tenants before we allowed to set the starting/ending time to polls.
We aren't adding any tests for these tasks because tests for rake tasks
are slow and tests creating tenants are also slow, making the
combination of the two even slower, particularly if we add tests for
every single task we're changing. We're adding tests for the
`.run_on_each` method instead.
There's no point generating stats nobody can access.
Note with this change we're automatically excluding polls created in the
dashboard, since these polls don't have stats enabled.
We're generating stats every 2 hours because it's less than the time it
will take to generate stats for every process. Once stats are generated,
this task should take less than a second.
The regenerate task has been added so we can manually execute it.
