Add an "all" field which expands to all fields of the report type.

Add an "all" field which expands to all fields of the report type.

For example in LVM2, "pv_all" gives all PV fields.
"seg_all" gives all LV segment fields.

"all" gives all fields of the final report type.  I think this is more
useful than just adding the current prefix.

So "lvs -o seg_all" gives all the LV segment fields, whilst
"lvs --segments -o all" adds in LV and VG fields too.

"lvs -o all -O vg_name" has report type LVS+VGS so includes all LV and all
VG fields.