Attachments_get_by_host|instance should be just that, associating
them with a specified volume-id doesn't really solve the problem.
If that relationship is needed a simple get_by_volume will work with
some inspection.
This patch removes the volume_id arg from those get methods. A follow
up patch will add get_all with filters for more complex relationships.
Change-Id: Ic5ffdced96fdf780cce2a1227c5f2a599860f0ca
Closes-Bug: #1632433
6f174b4126