fixes:
  - |
    Extremely large instance images, post eventlet removal, were causing CPU
    spikes and the conductor process to hang while the image was being
    fetched and validated. This optimizes the instance fetch and validation
    in two ways -- first, we now calculate the image checksum while the
    file is being fetched instead of as a separate step. Secondly, we were,
    in some cases, using the default chunk size of 128 bytes during downloads.
    Now, we use a more standard and reasonable value of 1 megabyte.
