Run n-cpu using LXD_GROUP when LXD virt driver

Enabling nova-lxd require to run n-cpu using lxd group

Change-Id: I0553dafcc797fcc1342501a558c7455261cf3daf
diff --git a/stackrc b/stackrc
index acb7d3f..b5d1bc0 100644
--- a/stackrc
+++ b/stackrc
@@ -586,6 +586,9 @@
             LIBVIRT_GROUP=libvirtd
         fi
         ;;
+    lxd)
+        LXD_GROUP=${LXD_GROUP:-"lxd"}
+        ;;
     fake)
         NUMBER_FAKE_NOVA_COMPUTE=${NUMBER_FAKE_NOVA_COMPUTE:-1}
         ;;