Missing LVM package install step on Ubuntu

The Cinder Block Storage service node guide was missing a
step to install the lvm2 packages. These packages needed
to be installed before the pvcreate and vgcreate steps
were initiated.

Change-Id: I7b85b962f8652667dd9df18b470430f9063a89f8
backport: havana
Closes-Bug: 1259443
Merge "Missing LVM package install step on Ubuntu"