Add the 'delete_on_termination' field to the volume attach API to support
configuring whether to delete the data volume when the instance is destroyed.
To avoid upgrade impact issues with older computes, the
'delete_on_termination' field is set in the API rather than when the BDM
is created in the compute service.
Implements: blueprint support-delete-on-termination-in-server-attach-volume
Change-Id: I55731b1822a4e32909665a2872d80895cb5b12f7
e5b47543cf