md component detection addition in vg_read

md component detection addition in vg_read

Usually md components are eliminated in label scan and/or
duplicate resolution, but they could sometimes get into
the vg_read stage, where set_pv_devices compares the
device to the PV.

If set_pv_devices runs an md component check and finds
one, vg_read should eliminate the components.

In set_pv_devices, run an md component check always
if the PV is smaller than the device (this is not
very common.)  If the PV is larger than the device,
(more common), do the component check when the config
setting is "auto" (the default).