Pass SOFT flag on delete of MIF-image

[jamoore]

Once #10776 has been implemented, attempting to delete a single image from a MIF will result in an exception ("foreign key constraint"). If the SOFT flag is passed for the /Image/Fileset relationship, then the delete of the main image can proceed without affecting the rest of the MIF. It's unclear whether:

• SOFT should always be passed;
• MIFs should be detected and SOFT passed; or
• An attempt made without SOFT with a dialog provided to the user explaining the situation (possibly with highlighting, see #10778) and a confirmation to use SOFT. This would depend on a clear explanation of the situation in the ERR object returned by graph deletes (#10776)

Either of the first 2 options would be an initial win.

[wmoore]

In discussion with Josh:

• Always use 'SOFT' (clients don't have to know about this)
• Clients need to handle return message, E.g. {"remaining-filesets":[596, 492]}. See #10806

[jamoore]

Just to be clear, the clients (or at least the gateways) will need to be aware because SOFT will need to be passed for DELETE but not for CHGRP. (At least that's the fastest way to have this implemented. Perhaps we can hard code the difference server-side)

[jamoore]

Server-side changes for #10776 have made this unnecessary. Closing.