Allow for missing trusts for Magnum cluster deletion

[mnaser]

In the referenced issue, we are failing to delete a cluster because the trust is already gone, we should handle that exception and just pass through if it's already gone instead of failing because we can't delete something that already doesn't exist.

[ricolin]

https://review.opendev.org/c/openstack/magnum/+/852993

[mnaser]

@ricolin looks clean, +2 from my side, I guess you'll have to shop other reviews :)

[mnaser]

@ricolin looks like it landed, wanna push up some back ports too and put them here?

[ricolin]

This merged today, will push for stable branches

[ricolin]

okay stable branch merged https://review.opendev.org/c/openstack/magnum/+/854136
thanks @mnaser

[ricolin]

I guess we can close this now.

[mnaser]

@ricolin indeed, this can be closed, but also with magnum-cluster-api, we're leveraging appcreds instead which should be much neater.