Race condition with the object-store relation

[Ionut-Madalin Balutoiu]

The `CONFIGS.write(GLANCE_SWIFT_CONF)` is missing in the `object_store_joined` hook. This config file is used when the `swift` backend is enabled.

This bug is only encountered on some deployments, because there are multiple places where `CONFIGS.write_all()` is called.

If the `object-store` relation is established, and another hook calls `CONFIGS.write_all()`, this problem wouldn't reproduce. However, if `object-store` relation is executed last, this issue will pop up.

[Ionut-Madalin Balutoiu (ionutbalutoiu)]

@Alex

I already fixed this into:
* https://review.opendev.org/c/openstack/charm-glance/+/774907

And since I was at it, I updated testing as well with:
* https://review.opendev.org/c/openstack/charm-glance/+/775197
* https://github.com/openstack-charmers/zaza-openstack-tests/pull/505

[Alex Kavanagh (ajkavanagh)]

Review to fix the bug:
https://review.opendev.org/c/openstack/charm-glance/+/777764

[Ionut-Madalin Balutoiu (ionutbalutoiu)]

The fix for this issue was merged: https://review.opendev.org/c/openstack/charm-glance/+/774907