Add API validation schema for volume_attachments

This patch adds API validation schema for volume_attachments.

Update volume required only Volume Id in request body but sample
files used to pass 'device' also.
This patch also correct those API sample files-
doc/v3/api_samples/os-volumes/update-volume-req.json
nova/tests/functional/v3/api_samples/os-volumes/update-volume-req.json.tpl

DocImpact

Partially implements blueprint v2-on-v3-api

Change-Id: I489272528fe4f4c43ab781d6a1a46742b1702c76
Merge "Add API validation schema for volume_attachments"