Find available loop device for cinder-volumes

Previously, Packstack used a fixed loop device (/dev/loop2) to create
the cinder-volumes test volume. This could create a conflict if the
loop device was already in use.

Using 'losetup -f' to find an available loop device should fix this.

Change-Id: Ie175e9f6127cfcdce6eda95a67051dda9c64104f
Closes-Bug: #1555454

packstack/puppet/templates/cinder_lvm.pp

@@ -1,9 +1,12 @@
 $create_cinder_volume = hiera('CONFIG_CINDER_VOLUMES_CREATE')
 
 if $create_cinder_volume == 'y' {
+    # Find an available loop device
+    $loop_dev = chomp(generate('/usr/sbin/losetup', '-f'))
+
     class { '::cinder::setup_test_volume':
       size            => hiera('CONFIG_CINDER_VOLUMES_SIZE'),
-      loopback_device => '/dev/loop2',
+      loopback_device => $loop_dev,
       volume_path     => '/var/lib/cinder',
       volume_name     => 'cinder-volumes',
     } ->