LVM-activate: align dmsetup report command to standard

Namely to change 'vgname/lvname' to 'vg_name/lv_name'. The dmsetup
report command follows lvm2 selection criteria field name standard.

• dmsetup v1.02.86 (lvm2 v2_02_107) - 23rd June 2014 "Add dmsetup -S/--select to define selection criteria"
• dmsetup info -c -S help

Signed-off-by: Roger Zhou <zzhou@suse.com>