Fix incorrect install location of networking default file

Ticket: none
Reviewed By: roopa,satish
Testing Done: built, installed, verified correct location

The install file resulted in creating /etc/default/networking/ as a
directory and installing the networking.default file in it.  Rename
networking.default to networking, and change the install file.
Normally dh_installinit handles all this, but since the package is
ifupdown2, and the file is networking, that doesn't happen.

Also, because we had created a directory with the name of what we want
to install as a file, we need to remove it if it exists.  This addition
of a preinst file should not go upstream, and should be removed in a few
weeks when everybody has re-installed enough.

debian/ifupdown2.install

@@ -1,3 +1,3 @@
 sbin/ifupdown2 /usr/share/ifupdown2/
 sbin/start-networking /sbin
-debian/networking.default /etc/default/networking
+debian/networking /etc/default/

debian/ifupdown2.preinst

@@ -0,0 +1,13 @@
+#! /bin/sh
+set -e
+case "$1" in
+    install|upgrade)
+        # workaround 3.0.0 internal install error.  This can be removed in a
+        # few weeks.
+        if [ -f /etc/default/networking/networking.default ]; then
+            dpkg-maintscript-helper rm_conffile /etc/default/networking/networking.default 1.1 -- $@
+            rm -rf /etc/default/networking
+        fi
+        ;;
+esac
+