rgw/CloudTransition: Tier objects to remote cloud

rgw/CloudTransition: Tier objects to remote cloud

If the storage class configured is of cloud, transition
the objects to remote endpoint configured.

In case the object size is >mulitpart size limit (say 5M),
upload the object into multiparts.

As part of transition, map rgw attributes to http attrs,
including ACLs.

A new attribute (x-amz-meta-source: rgw) is added to denote
that the object is transitioned from RGW source.

Added two new options to tier-config to configure multipart size -
* multipart_sync_threshold - determines the limit of object size,
when exceeded transitioned in multiparts
* multipart_min_part_size - the minimum size of the multipart upload part

Default values for both the options is 32M and minimum value supported
is 5M.

Signed-off-by: Soumya Koduri <skoduri@redhat.com>