Add LVM Cinder support

It relies on loopback devices and is only meant for testing.
diff --git a/linux/storage/loopback.yml b/linux/storage/loopback.yml
new file mode 100644
index 0000000..adbbe65
--- /dev/null
+++ b/linux/storage/loopback.yml
@@ -0,0 +1,8 @@
+parameters:
+  linux:
+    storage:
+      enabled: true
+      loopback:
+        loop0:
+          file: "/srv/disk0"
+          size: ${_param:loopback_device_size}G