Merge lp://staging/~niedbalski/charm-helpers/fix-1699565 into lp://staging/charm-helpers

Does this really need to be in charm-helpers? It seems to be something that could just be done in the glance charm. The function 'update_policy(...)' would have to also be mocked out in the glance charm to test the code that it will be using.

Are you seeing other use cases that means that it will be used across many charms? Thanks.

I agree with having this in charm-helpers, because I'm aware of at least 1 other charm that could benefit from this (keystone charm). We update the policy.json when v3 is enabled.

Okay, if it is needed, then it should have a more generic name. It's essentially updating a json file, not particularly a policy file, so:

    def update_json_file(filename, items):
        ....

would make it more usable from a re-use perspective. i.e. there's nothing in the function that dictates that it's a policy file only. And this is a utils library module.