Remove reattach function in cinder-manage

The reattach function in cinder-manage depends on
db.instance_get, which is not available in cinder db.
db.instance_get is only available in nova db. Hence, the
reattach function should be removed from cinder-manage.

Change-Id: If33bf2f281735bd530641c1e6d15e9645f38b4b4
Closes-Bug: #1167931