In the very rare case when all drives in a erasure set need to be healed,
remove .healing.bin from all drives, otherwise it will be stuck in a
loop
Also, fix a unit test that fails sometimes due to wrong test.
precondition check was being honored before, validating
if anonymous access is allowed on the metadata of an
object, leading to metadata disclosure of the following
headers.
```
Last-Modified
Etag
x-amz-version-id
Expires:
Cache-Control:
```
although the information presented is minimal in nature,
and of opaque nature. It still simply discloses that an
object by a specific name exists or not without even having
enough permissions.
