lvconvert: suppress zeroing warning when converting to thin

lvconvert: suppress zeroing warning when converting to thin

When volume was lvconvert-ed to a thin-volume with external origin,
then in case thin-pool was in non-zeroing mode
it's been printing WARNING about not zeroing thin volume - but
this is wanted and expected - so nothing to warn about.

So in this particular use case WARNING needs to be suppressed.

Adding parameter support for lvcreate_params.

So now lvconvert creates 'normal thin LV' in read-only mode
(so any read will 'return 0' for a moment)
then deactivate regular thin LV and reacreate in 'final R/RW' mode
thin LV with external origin and activate again.