Switch to pvs from pvck - it uses return codes

Using pvs rather than pvck means that we can test for a return code
of '5' rather than parsing output to discover whether a device is a PV.
Replace pvdisplay with pvs

As it has better output control
Switch to lvs, better output control
Switch to use vgs rather than vgdisplay

Better handling of output to just what we need (free & total PE count)