Fix mirrored stripe reduction.

Fix mirrored stripe reduction.

Patch adds check for stripe not only in direct
LV segment but also in mirror image segment.

This prevents bugs like:

# lvcreate -i2 -l10 -n lv vg_test
# lvconvert -m1 -i1 vg_test/lv

# lvreduce -f -l1 vg_test/lv
  WARNING: Reducing active logical volume to 4.00 MiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
  Reducing logical volume lv to 4.00 MiB
  Segment extent reduction 9 not divisible by #stripes 2
  Logical volume lv successfully resized

# lvremove -f vg_test
  Segment extent reduction 1 not divisible by #stripes 2
  LV segment lv:0-4294967295 is incorrectly listed as being used by LV lv_mimage_0
  Internal error: LV segments corrupted in lv_mimage_0.