TT#5444 Debian stretch doesn't have security support (yet)

While setting up sources.list for bootstrap stage has been take
care of in commit 24852d04eb already, the sources.list
generation before running ngcp-installer needs to be adjusted as
well.

Change-Id: I94f1cb8057c544e9df678a4f008abf713fa83da3

deployment.sh

@@ -1561,10 +1561,17 @@ EOF
 
 # Debian repositories
 deb ${MIRROR} ${DEBIAN_RELEASE} main contrib non-free
-deb ${SEC_MIRROR} ${DEBIAN_RELEASE}-security main contrib non-free
-deb ${MIRROR} ${DEBIAN_RELEASE}-updates main contrib non-free
 EOF
 
+if [ "$DEBIAN_RELEASE" = "stretch" ] ; then
+  echo  "Warning: not enabling security repository for $DEBIAN_RELEASE"
+  logit "Warning: not enabling security repository for $DEBIAN_RELEASE"
+else
+  echo "deb ${SEC_MIRROR} ${DEBIAN_RELEASE}-security main contrib non-free" >> "$TARGET"/etc/apt/sources.list.d/debian.list
+fi
+
+echo "deb ${MIRROR} ${DEBIAN_RELEASE}-updates main contrib non-free" >> "$TARGET"/etc/apt/sources.list.d/debian.list
+
   # support testing rc releases without providing an according installer package ahead
   if [ -n "$AUTOBUILD_RELEASE" ] ; then
     echo "Running installer with sources.list for $DEBIAN_RELEASE + autobuild release-$AUTOBUILD_RELEASE"