Add a script to delete old mirrored Pombola instances

[mhl]

This will look through all those databases that begin with one of:

popitkenyan-politicians popit_stagingkenyan-politicians popitza-peoples-assembly popit_stagingza-peoples-assembly

It will skip any that:

• Have a timestamp within the last three days
• Are currently in use for the corresponding popit instance

Any other database will be removed. It will remove both:

• The mongodb database
• The Elasticsearch index of the same name

Partial fix for: https://github.com/mysociety/Non-Site-Specific/issues/688

[chrismytton]

I wonder if it's worth adding a dry run flag so that remove_database just prints what it would remove? That way we can eyeball it before we run it for real. Other than that this looks good! :+1:

[mhl]

Thanks, @chrismytton - I've amended that commit to add a --commit option, so that the default is to not delete stuff unless you specify that option.

[chrismytton]

:+1: