Add an LVM interface to allow management on local nodes.

There are a number of projects that currently utilize LVM to create local (on node) storage resources. Creating a common LVM interface in openstack-common will limit the code duplication that we already have (ie nova.virt.libvirt.utils) but more importantly will lay the ground work to start doing some cooler things in terms of Cinder and storage scheduling placement.

The vision here is the ability to schedule block-storage resources on the compute node when a VG is available. So for folks that don't have high perf san devices, or just simply want locality specific storage they'll have the ability to create a persistent block storage device locally on the compute node and direct connect (bypassing iSCSI altogether).

Also, this module should be useful as we move forward with other projects like Triple-O/Ironic. Later additions of things like the initiator pieces in cinder.brick would be most useful and should be picked up by Nova and Manilla fairly quickly.