Enable using btrfs as a backend

Enable the usage of btrfs backend. Nothing is done except not using
lxd init as it only supports zfs and dir.

Change-Id: Ic6390e457b80a5d38957c182f270fc9f9d52a60f

defaults/main.yml

@@ -534,12 +534,16 @@ nova_compute_powervm_pip_packages:
 
 lxd_bind_address: 0.0.0.0
 lxd_bind_port: 8443
+
+# Supported backends are 'zfs', 'dir' and 'btrfs' for now.
+# To use btrfs, a btrfs filesystem must be mounted in /var/lib/lxd
+# during compute node configuration.
 lxd_storage_backend: dir
 # This needs to be set in the user_secrets.yml file.
 #lxd_trust_password:
 
 # This variable should be used with lxd when using a
-# storage backend that utilizes storage pools
+# storage backend that utilizes storage pools (zfs)
 #lxd_storage_pool:
 
 # PCI devices passthrough to nova

templates/lxd-init.sh.j2

@@ -1,6 +1,8 @@
 #!/bin/bash
 # {{ ansible_managed }}
 
+{% if (lxd_storage_backend == "zfs" or lxd_storage_backend == "dir") %}
+
 # This is a script to configure lxd system settings.
 # "/usr/bin/lxd init"
 
@@ -13,3 +15,14 @@
   --storage-pool={{ lxd_storage_pool }} \
 {% endif %}
   --trust-password={{ lxd_trust_password }}
+
+{% elif (lxd_storage_backend == "btrfs") %}
+
+# Check if filesystem if mounted as btrfs.
+# If not nothing happens and storage will still be set to dir by default
+
+if [ $(findmnt /var/lib/lxd -o FSTYPE -n) == "btrfs" ]; then
+  systemctl restart lxd
+fi
+
+{% endif %}