Move image_meta_to_headers from images_client

Glance v1 images_client contains image_meta_to_headers() which
converts a dict to headers. However, most service clients'
methods don't convert like that.
Then this moves image_meta_to_headers() to common place like
the compute module from the service client.

Partially implements blueprint consistent-service-method-names

Change-Id: Id8e47fd35f7667578854bc439238a4b0f36fbb8f
9 files changed