Allow to use a custom block device with LXD init

Also add a missing package when using LXD with LVM backend which is not
yet fully configurable, see:
https://bugs.launchpad.net/openstack-ansible/+bug/1678073

Change-Id: I384a8aa7713946b349fcf34dfb7d62ae2177ae2d

defaults/main.yml

@@ -541,6 +541,10 @@ lxd_storage_backend: dir
 # This variable should be used with lxd when using a
 # storage backend that utilizes storage pools
 #lxd_storage_pool:
+# This variable should be used with lxd when using a
+# storage backend that utilizes storage pool if you
+# want to use a specific bloc device instead of loop
+#lxd_storage_create_device: "/dev/sdb"
 
 # PCI devices passthrough to nova
 # For SR-IOV please use:

templates/lxd-init.sh.j2

@@ -11,5 +11,8 @@
   --storage-backend={{ lxd_storage_backend }} \
 {% if lxd_storage_pool is defined %}
   --storage-pool={{ lxd_storage_pool }} \
+{% endif %}
+{% if lxd_storage_create_device is defined %}
+  --storage-create-device={{ lxd_storage_create_device }} \
 {% endif %}
   --trust-password={{ lxd_trust_password }}

vars/ubuntu-16.04.yml

@@ -70,6 +70,7 @@ nova_compute_lxd_distro_packages:
   - python-libguestfs
   - sysfsutils
   - vlan
+  - thin-provisioning-tools
 
 nova_nginx_distro_packages:
   - nginx-full