lvconvert: add new reporting fields for reshaping

lvconvert: add new reporting fields for reshaping

During an ongoing reshape, the MD kernel runtime reads stripes relative
to data_offset and starts storing the reshaped stripes (with new raid
layout and/or new stripesize  and/or new number of stripes) relative
to new_data_offset.  This is to avoid writing over any data in place
which is non-atomic by nature and thus be recoverable without data loss
in the transition.  MD uses the term out-of-place reshaping for it.

There's 2 other areas we don't have report capability for:
- number of data stripes vs. total stripes
  (e.g. raid6 with 7 stripes toal has 5 data stripes)
- number of (rotating) parity/syndrome chunks
  (e.g. raid6 with 7 stripes toal has 2 parity chunks; one
   per stripe for P-Syndrome and another one for Q-Syndrome)

Thus, add the following reportable keys:

- reshape_len      (in current units)
- reshape_len_le   (in logical extents)
- data_offset      (in sectors)
- new_data_offset  (     "    )
- data_stripes
- parity_chunks

Enhance lvchange-raid.sh, lvconvert-raid-reshape-linear_to_striped.sh,
lvconvert-raid-reshape-striped_to_linear.sh, lvconvert-raid-reshape.sh
and lvconvert-raid-takeover.sh to make use of new keys.

Related: rhbz834579
Related: rhbz1191935
Related: rhbz1191978