Deleted account respond as non existing accounts

Currently clients can not distinguish between non existing accounts
(which can be created) and accounts marked for deletion, which has
not yet been reaped and therefore cannot be re-created until reaped.

Following this patch, if an account is marked as deleted but hasn't
been reaped and is still on disk, responses will include a status
header:
    'X-Account-Status' = 'Deleted'

Fixes:Bug #1188609
Change-Id: Ibd39965ae3f5d45fd78f130e0e31f5a0141a8633