Refactor cagg_migrate regression tests

This is a small refactoring to create a new old format Continuous
Aggregate named `conditions_summary_weekly` instead of drop and create
again the same `conditions_summary_daily`.

It will be necessary for the upcoming patch for the removal of the old
format where we'll need to manually create old format Continuous
Aggregates by restoring it from an SQL script in order to keep this
regression tests working.

Signed-off-by: Fabrízio de Royes Mello <[email protected]>