These all belong in separate files. Make it so.
We also rename the volume_attachment schema file to volume_attachments,
to better link it to the actual API code, and tweak an error message to
fix some capitalization.
Change-Id: Iffefc263bbf19d18137207c0432c16fdb3c513f9
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>