This PS adds loopback device support to the gate scripts.
Rather than using simple loopback devices we use iscsi to
allow is to target the created devices via the bus they are
connected to. An arbitary number of devices of a desired size
can be created, and controlled via env vars.
Change-Id: I05fb7f3a1564bc36903aed2c46ed996bb8cc57c8
fdbe8eb60d