backport: S3 policy evaluated incorrectly

[Jesse Williamson]

[Impact]
If a user tries to access a non-existent bucket, it should get a 'NoSuchBucket' error message (404)
But if there is such a bucket which is belonged to another user, radosgw will return 'AccessDenied' error (403)
This is an incorrect error message, radosgw should return 404

[Test Case]
Create a user by radosgw-admin, then create a bucket through S3 by this user
Create another user and try to access the bucket created by the above user
The error message must be 'NoSuchBucket', not 'AccessDenied'

[Regression Potential]
Low, this patch checks
1. 'is_admin_of' and 'verify_permission' separately instead of 'and' the results of them
2. if the bucket policy allow the user to access this bucket
to make sure it returns the correct error code, so basically it checks the same thing as before but in the correct order

[Other Information]
Backport Ceph issue 38638 to Luminous.

If a user different from the owner (or even an anonymous user) does a GetObject/HeadObject on a non existing object, Radosgw returns status code 403, rather than the correct status 404.

A version of this was merged into Ceph master:
https://tracker.ceph.com/issues/38638
https://github.com/ceph/ceph/commit/5eb50b7d10da51db72f705807c87775562b79b63

And backported to luminous has been accepted:
https://tracker.ceph.com/issues/39272
https://github.com/ceph/ceph/commit/a752b21f549cc83745e35324387b85b3d039dfd2

[gerald.yang (gerald-yang-tw)]

Disco, Eoan and Focal has already included this fix

[gerald.yang (gerald-yang-tw)]

bionic patch

[Ubuntu Foundations Team Bug Bot (crichton)]

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[James Page (james-page)]

Uploaded to bionic-proposed for SRU team review.

[James Page (james-page)]

Fix included in recent point release (bug 1861793) - closing this bug as will be covered by upstream testing and general regression testing for point release.