xenserver: Give ovs-vsctl a bit more time to do its work

Creating bonds sometimes fails due to ovs-vsctl timing out.  This commit
increases the time interface-reconfigure gives ovs-vsctl from five to
twenty seconds.  We should investigate why it's taking ovs-vsctl so
long, but this helps for now.

xenserver/opt_xensource_libexec_interface-reconfigure

@@ -1255,7 +1255,7 @@ def datapath_modify_config(commands):
         for c in commands:
             log("  %s" % c)
 
-    rc = run_command(['/usr/bin/ovs-vsctl']
+    rc = run_command(['/usr/bin/ovs-vsctl'] + ['--timeout=20']
                      + [c for c in commands if not c.startswith('#')])
     if not rc:
         raise Error("Failed to modify vswitch configuration")