Install netcat for libvirt live migration

Libvirt live migration requires netcat. It appears that newer UCA
packages may not automagically pull this in so explicitly list it as a
dependency of nova compute here. Note that netcat/netcat-traditional do
not appear to work and netcat-openbsd is required.

Change-Id: If2dbc53d082fea779448998ea12b821bd037a14e
diff --git a/files/debs/n-cpu b/files/debs/n-cpu
index 69ac430..d8bbf59 100644
--- a/files/debs/n-cpu
+++ b/files/debs/n-cpu
@@ -2,6 +2,7 @@
 genisoimage
 gir1.2-libosinfo-1.0
 lvm2 # NOPRIME
+netcat-openbsd
 open-iscsi
 python-guestfs # NOPRIME
 qemu-utils