The 'force' parameter of os-brick's disconnect_volume() method allows
callers to ignore flushing errors and ensure that devices are being
removed from the host.
We should use force=True when we are going to delete an instance to
avoid leaving leftover devices connected to the compute host which
could then potentially be reused to map to volumes to an instance that
should not have access to those volumes.
We can use force=True even when disconnecting a volume that will not be
deleted on termination because os-brick will always attempt to flush
and disconnect gracefully before forcefully removing devices.
Closes-Bug: #2004555
Change-Id: I3629b84d3255a8fe9d8a7cea8c6131d7c40899e8
db455548a1