RFE: Support LVM thin provisioning

[opoplawski]

koan checks to see if there is free space in the volume group before proceeding and fails if there isn't, e.g.:

volume group needs 10 GB free space.

This can fail improperly in two situations - if the LV already exists, or if one is using thin provisioning and all space is allocated to the thin pool (although the only way to currently make use of thin provisioning is to create the needed LV before running koan).

At least as a first step, I think we should just remove the space check entirely and rely on errors from LVM if there is not enough space. Longer term it would be good to support the needed thin provisioning options.