Fix detection of LVM2 PV busy status when exported VGs exist (#160787)

If a Volume Group is exported the "lvm lvs" command returns non-zero
exit status causing its output to not be loaded into the LVM2_PV_Info
cache and detection of busy Physical Volumes completely fail.

    # lvm lvs -o lv_name,vg_name,lv_attr
      Volume group GParted_VG4 is exported
      LV    VG          Attr
      lvol0 GParted-VG2 -wi---
      lvol0 GParted_VG3 -wi-a-
      lvol1 GParted_VG3 -wi-a-
    # echo $?
    5

Switch to using "lvm pvs" to query all cached information using one
command, which doesn't return non-zero when exported VGs exist.

    # lvm pvs --nosuffix --units b -o pv_name,pv_free,vg_name,lv_name,lv_attr
      PV         PFree      VG          LV    Attr
      /dev/sda10 2147483648
      /dev/sda11 2143289344 GParted-VG1
      /dev/sda12 1619001344 GParted-VG2 lvol0 -wi---
      /dev/sda12 1619001344 GParted-VG2
      /dev/sda13  830472192 GParted_VG3 lvol0 -wi-a-
      /dev/sda13  830472192 GParted_VG3 lvol1 -wi-a-
      /dev/sda13  830472192 GParted_VG3
      /dev/sda14 1619001344 GParted_VG4 lvol0 -wi---
      /dev/sda14 1619001344 GParted_VG4
    # echo $?
    0

Bug #160787 - lvm support