Filter out LVM block devices for cinder

Cinder may create physical LVM volumes which might be picked up by the
operating system and treated the wrong way. We can be explicit in the
filter and only allow our loopback device to be seen by pvscan.

Change-Id: I73a5b8ed0c3989ff61a3005cb70acd8a95532271
Closes-Bug: #1261422
Make cinder loopback config idempotent

If this script is run twice for some reason, it will attach more and
more loopback devices to the backing file which is problematic. Using -j
will use the first device if one has already been attached.

Change-Id: Idcc84b308e1edcdb9ab819f2f4a5fc465ef5661e
Make cinder buildable stand-alone

Cinder needs some python modules that make use of libssl-dev for
installation.

Change-Id: Ib9c74e89683ddf6600a0492235b96b8083e3b7f4