Convert Cinder to use openstack-common jsonutils.

Convert Cinder to use openstack-common jsonutils.

This patch replaces json handling code in Cinder with openstack-common
jsonutils.  Also remove some unused imports.

Implement blueprint cinder-common-jsonutils

Change-Id: I28c1a095823c2f04f30c32724144297a2d67fba4
Reviewed-on: https://review.openstack.org/9912
Reviewed-by: Mark McLoughlin <markmc@redhat.com>
Reviewed-by: Vish Ishaya <vishvananda@gmail.com>
Approved: John Griffith <john.griffith@solidfire.com>
Tested-by: Jenkins