Add purge flag in image_meta_to_headers

When calling image_client_v1's update_image with "purge" flag,
it raise 400 Bad Request with message "Bad header: x-image-meta-purge-props".
This is to add purge transform in image_meta_to_headers to support purge flag.

Change-Id: I2a30c2fc746701805f9e9cc77068c7eaa17dbcb8
Closes-Bug: #1597591
2 files changed