XenAPI: Use XenServer DevStack plugins

Hypervisor XenServer will change to use os-xenapi in the future,
this will need DevStack changes, this patch is to remove install
Dom0 plugins part to our own DevStack plugins.

Change-Id: Ic327135b893a77672fd42af919f47f181e932773
diff --git a/tools/xen/xenrc b/tools/xen/xenrc
index bb27454..2161247 100644
--- a/tools/xen/xenrc
+++ b/tools/xen/xenrc
@@ -101,6 +101,7 @@
 
 ## Note that the lines below are coming from stackrc to support
 ## new-style config files
+source $RC_DIR/functions-common
 
 # allow local overrides of env variables, including repo config
 if [[ -f $RC_DIR/localrc ]]; then