Switch to using lvs to identify active LVM LVs (#160787)

Previously used "dmsetup info" to directly list device-mapper mapping
names in the kernel to identify active Logical Volumes.  However GParted
failed to recognise active LVs if the VGNAME contains any hyphens (-).
This is because LVM encodes hyphens as double hyphens in the mapping
name.

To avoid having to duplicate the LVM hyphen encoding in GParted, switch
to using "lvm lvs" to list LVs.

    # dmsetup info --columns --noheadings --separator , -o name
    GParted_VG1-lvol_00
    GParted--VG2-lvol--00

    # lvm lvs --noheadings --separator , -o lv_name,vg_name,lv_attr
      lvol_00,GParted_VG1,-wi-a-
      lvol-00,GParted-VG2,-wi-a-
      lvol-01,GParted-VG3,-wi---
                             .^.
(-) not active, (a) or any other character considered active.  Reference
lvs(8).

Bug #160787 - lvm support