Devmapper: parallelize device close/deactivate

waitClose will wait for one second and then timeout waiting for a
device to close.  If many devices will not close, for whatever reason,
each of those one second waits happen serially and causes daemon
shutdown to become annoyingly slow.

This parallelizes the close/deactivate so that each device will still
have a one second timeout, but the aggregate wait for all devices
comes down to one second of wall time as well.