ceph-volume: add some flexibility to bytes_to_extents

ceph-volume: add some flexibility to bytes_to_extents

For batch we want to report the projected sizes before creating any LVM
structures, we use the device size for that. This means we pass this
projected size to lvm/api.py::create_lv. This could result in situations
where we request more extents for the new LV than are actually
available, as LVM takes up some available space on the block device
(plus alignment).
We fix this by adjusting the extent count downwards if its less than 1% off the
requested value.

Fixes: https://tracker.ceph.com/issues/47758
Signed-off-by: Jan Fajerski <jfajerski@suse.com>