rgw: resharding causes bucket attributes to be lost

rgw: resharding causes bucket attributes to be lost

With the new resharding code, some bucket metadata that is stored as
xattrs (e.g., ACLs, life-cycle policies) were not sent with the
updated bucket instance data when resharding completed. As a result,
resharding has a regression where that metadata is lost after a
successful reshard.

This commit restores the variable in the RGWBucketReshard class that
maintains the bucket attributes, so they can be saved when the bucket
instance object is updated.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>