rackerlabs/deuce — pull request #161 by TheSriram (2014-09-22 17:43:28+00:00)
Title: feat: HEAD /blocks/{block_id} endpoint

on a HEAD, the block is checked for existence in the metadata store,
after which its checked for existence in block storage.

- If present in metadata, and non-existent in block storage:
502 Bad Gateway is returned along with an explanation.

- If present both in metadata and block storage.:
200 OK is returned along with headers such as
x-block-reference-count

- If not present in metadata:
404 Not Found is returned