Move apply_chunk_growth outside of a for-cycle

Otherwise it is for no reason defined again and again. Prepend an underscore to
its name to mark it private.

Related: rhbz#1093144
Take extra RAID metadata into account when growing LV (#1093144)

If we create an LV in a VG that has one or more of its PVs on top of RAID, we
add 5 extra PEs per disk for the metadata. So when growing an LV we should take
that into account and shrink the available pool size with those extents.
Do not limit ThinLV's size to VG's free space

ThinLV takes extents from a thin pool LV not from its VG.