Size and checksum should be immutable for active images

[Stuart McLaren]

> > > There are cases where an image's 'size' or 'checksum' values need to be
> > > modified before an image becomes active; but do we need, as I think we
> > > currently do, to allow users to change them once an image becomes
> > > active?
> > >
> > > Without the 'size' pinned down an operator can't necessarily trust the
> > > current value.

[Brian Waldon (bcwaldon)]

https://review.openstack.org/#/c/40619/

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