Any sort of symlink could be used for inclusion into an lvm vg but lvm's
pvdisplay may show a real device name, or a mapper device name which is
a symlink.
Since we're interested in finding out if the actual device is part of
our volgroup, we test the realpath of both the device requested and the
device returned by pvdisplay to ensure they're the same device.
Fixes#26867 and #30882