Update invirt-dns to version 0.0.16

Requested by mitchb/root@ATHENA.MIT.EDU

diff --git a/invirt-dns b/invirt-dns
index b8f8534..c13d8c6 160000 (submodule)
--- a/invirt-dns
+++ b/invirt-dns
@@ -1 +1 @@
-Subproject commit b8f8534651b1ba734dc184efbf8f2c0e8c6e08bc
+Subproject commit c13d8c69b179a728a940185b6e3643722425a3d8