Restore permissions when dropping and recreating a matview

[corviday]

When a materialized view is changed by a migration, the view is DROPped and then CREATEd. The newly created version does not inherit the permissions the DROPped view had.

Recently we had this issue with the upgrade of vars_per_history_mv . It was fixed with the following command:

grant select on crmp.vars_per_history_mv to viewer;

This command should be incorporated into migration 3505750d3416 for both upgrades and downgrades.

[rod-glover]

1. Yes.
2. There's a handy bit of tooling that incorporates much of the work, including indexes and privilege management, into single calls. Those calls are create_matview and drop_matview. For example usages, see https://github.com/pacificclimate/pycds/blob/master/pycds/alembic/versions/bb2a222a1d4a_convert_obs_count_per_month_history_mv_.py .

[rod-glover]

There are several other migrations that use these utility methods as well, for additional examples.