We've had an lvm_type=thin for quite some time, and we've wanted to
make it Cinders default for a while, but there's no clean way to
migrate on upgrades. So, we have a compromise, detect if the
deployment has volumes (including the thin pool). If there are no
LVs or if the thin pool exists, use thin. Otherwise, use the old
thick lvm-default.
This patch makes the default setting "auto" instead of "default"
(which is actually thick).
DocImpact: Need to update docs to reflect the default setting for
new deployments is auto (thin)
Change-Id: If25e814eb6282fef9a1dd30d17c80eab6860e275
8c57c6d3ee