Convert libvirt connection class to use config APIs for filesystem devices

Remove the <filesystem> element from the Cheetah XML template
and make the libvirt connection class use the LibvirtConfigGuestFilesys
class for it instead

blueprint libvirt-xml-config-apis
Change-Id: I9dad031703161d1dff86af03eff7b1ebf657fc0c
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

nova/virt/libvirt.xml.template

@@ -58,12 +58,7 @@
 #end if
     <vcpu>${vcpus}</vcpu>
     <devices>
-#if $type == 'lxc'
-        <filesystem type='mount'>
-            <source dir='${basepath}/rootfs'/>
-            <target dir='/'/>
-        </filesystem>
-#else
+#if $type != 'lxc'
     #if $getVar('rescue', False)
         <disk type='file'>
             <driver type='${driver_type}' cache='${cachemode}'/>

nova/virt/libvirt/connection.py

@@ -1372,6 +1372,15 @@ class LibvirtConnection(driver.ComputeDriver):
         for (network, mapping) in network_info:
             cfg = self.vif_driver.plug(instance, network, mapping)
             devs.append(cfg.to_xml())
+
+        if FLAGS.libvirt_type == "lxc":
+            fs = config.LibvirtConfigGuestFilesys()
+            fs.type = "mount"
+            fs.source_dir = os.path.join(FLAGS.instances_path,
+                                         instance['name'],
+                                         "rootfs")
+            devs.append(fs.to_xml())
+
         # FIXME(vish): stick this in db
         inst_type_id = instance['instance_type_id']
         inst_type = instance_types.get_instance_type(inst_type_id)