rgw_file: fixup attrs across renames

rgw_file: fixup attrs across renames

Once Unix attributes were materialized as RGW object/bucket
attributes, it became possible to verify the serialized bucket and
object hashes with the expected values (based on the file-type
invariant path to the object).

Prior to this change, we saved the serialized hash values with the
rest of the Unix attrs, in RGW_ATTR_UNIX1.  Unfortunately, these
values were invalidated by rename operations.  To address this problem,
and to faciliate future operations on objects by their hashed ids,
the id hashes have been moved into their own RGW attr
RGW_ATTR_UNIX_KEY1.  This should allow more efficient search by, but
more importantly to the invalidation problem, allows us to use the
ATTRSMOD_MERGE behavior in RGWCopyObj to get copy offload while still
fixing up the object id.

The code at this commit doesn't use the serialized unix_mode value as
the outgoing st.st_mode result for rgw_getattr operations, pending a
bugfix for Ganesha's expected value range.

Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>