devices: refresh device ids if the system changes

devices: refresh device ids if the system changes

If the system changes, locate PVs that appear on different devices,
and update the device IDs in the devices file.  A system change is
detected by saving the DMI product_uuid or hostname in the devices
file, and comparing it to the current system value.  If a root PV
is restored or copied to a new system with different devices, then
the product_uuid or hostname should change, and trigger lvm to
locate PVIDs from system.devices on new devices.