Eager load columns in volume_get_active_by_window

Eager load columns in volume_get_active_by_window

All other volume-related methods in db.sqlalchemy.api are eager loading
volume_metadata, volume_admin_metadata (if admin), volume_type,
volume_attachment and consistencygroup. volume_get_active_by_window
wasn't, causing fails because of SQLAlchemy Session being closed when
trying to lazy load volume_metadata. This commit adds missing
options(joinedload()) to this query.

Change-Id: I33ec89d7f1f43aae6010aaa6e12951b7c522b8f0
Closes-Bug: 1517763
Related-Bug: 1501838