Test these LVM commands

[djs55]

We need simple regression tests for these LVM commands:

Note: not all of these commands may be implemented yet: see #16

• lvchange /dev/vg/lvname -p {r/rw}
• lvchange --addtag | --deltag 'hidden'
• lvchange --refresh
• lvcreate -n [-l <size_in_percentage> | -L <size_in_mb>] vgname --addtag
• lvdisplay <vg/lv> or </dev/vg/lv> or </dev/mapper/vg--lv> etc, output ignored
• lvdisplay -c - comma separated, used to get size (7th field, in sectors)
• lvremove -f --config devices{<devices?>}
• lvrename vg/lvname newname
• lvresize -L newsize /dev/vg/lvname
• lvs --noheadings /dev/vg/lvname (output ignored)
• lvs --noheadings --units b -o +lv_tags -- eg:
  test-lv-999 vg -wi-a---- 4194304B foo,bar,bzqa
• pvcreate --metadatasize 10M /dev/path
• pvremove device
• pvresize device
• pvs --noheadings --nosuffix --units b - use size (field 5) and free space (field 6)
• pvs --noheadings -o vg_name <pv name?>
• pvs
• vgchange -a[n|y] vgname
• vgcreate vgname /root/device
• vgextend vgname /dev/path
• vgremove vgname
• vgs (output ignored)
• vgs --noheadings --nosuffix --units b - use size (field 6) and free space (field 7)