Various Linux local blockstore changes:

Most important: if a <2TB blockstore has an ext4 filesystem, make sure we
create it without the 64bit and huge_file features. The former will make
it impossible (currently) to take a snapshot since imagezip does not handle
64-bit blocknumbers (working on it...)

Don't stripe an LVM LV over more than 8 devices. Some of the Clemson nodes
have 20+ disks and we won't buy much (and it might even be counterproductive)
to try to stripe writes over all devices all the time.

Still trying to get lvcreate to not prompt when one of the devices has an
old metadata prompt. -Zy is supposed to prevent that, but it doesn't. Try
adding -y as well.

Not related: in the BEGIN block, don't cat $ETCDIR/genvmtype unless it
actually exists. Not everything is a docker container ya know...