Missing CORS headers when write actions are rejected

[asaunier]

See also c2corg/v6_ui#1989 (comment)

Tested in prod, demo and in a personal instance:

• if a write action is accepted, nothing special is reported on the UI side in browsers' dev consoles
• on the other hand, if the write action is rejected (blocked or rate limited user, 500 error?), the UI error processing is not performed as expected (Add support of rate limiting message v6_ui#1989) and CORS errors are reported in the browsers' dev consoles:

It seems CORS headers are not returned when an exception is raised while processing the request.

• failed request (user is blocked):

• successful request:

[asaunier]

See investigations about CORS starting at c2corg/v6_ui#1989 (comment)

[lbesson]

see #1073 and Cornices/cornice#115

Updating cornice will probably solve the issue.