bdev: implement disk resize for lvm/drbd8

This patch implements disk resize at the bdev level for the LVM and
DRBD8 disk types. It is not implemented for DRBD7 and MD since the way
MD works with its underlaying devices makes it harder and this
combination is also deprecated.

The LVM resize operation is tried three times, with different allocation
policies:
  - contiguous first, since this is best for allocation purposes (it
    won't fragment too much the PV)
  - cling, which is supported only by more recent LVM versions, will try
    to place the new extents on the same PV as the rest of the LV
  - and finally normal, which is the default

Reviewed-by: imsnah