rgw/CloudTransition: Verify if the object is already tiered

rgw/CloudTransition: Verify if the object is already tiered

Add class to fetch headers from remote endpoint and verify if the object
is already tiered.

& Few other fixes stated below -

* Erase data in the head of cloud transitioned object
* 'placement rm' command should erase tier_config details
* A new option added in the object manifest to denote if the
  object is tiered in multiparts

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