Description of problem:

Add support for converting a normal LV into a thin volume, where the LV will be used as data volume for thin pool.

Currently the user can only use 'external-origin' feature, which uses normal LV as a read-only origin for unprovisioned blocks.

Also we might be eventually able to even convert thin-volume into a normal LV for the case there is only a single range-mapping for a thin LV (in terms of kernel thin metadata).

This would allow very easy use of temporary thin volumes instead of old-snapshot.

Estimated syntax to convert normal LV into thin LV

lvconvert -T vg/normal_lv   [--poolmetadasize,--chunksize... ]

Estimated syntax to convert thin LV into a normal LV (if possible)

lvconvert --type linear vg/thin_lv

I assume the internal logic may allow to use even options like 
-m0 or --type mirror, --type raid -  to convert thin into all other traditional
old-school formats....

Version-Release number of selected component (if applicable):
2.02.105

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