Provide an option to run tests with -proposed enabled

This reproduces #69. Don't enable it for CI as this is too unreliable in
general.

Author: martinpitt

tests/run-ubuntu-chroot

@@ -41,6 +41,9 @@ cat <<EOU > /etc/apt/sources.list
 deb http://archive.ubuntu.com/ubuntu ${RELEASE} main universe
 deb http://archive.ubuntu.com/ubuntu ${RELEASE}-updates main universe
 EOU
+if [ -n "${PROPOSED:-}" ]; then
+    echo "deb http://archive.ubuntu.com/ubuntu ${RELEASE}-proposed main universe" >> /etc/apt/sources.list
+fi
 apt-get update
 apt-get install -y pkg-config dh-autoreconf valac libglib2.0-dev libudev-dev libgudev-1.0-dev python3-gi gobject-introspection libgirepository1.0-dev gir1.2-glib-2.0 gir1.2-gudev-1.0 gtk-doc-tools udev xserver-xorg-video-dummy xserver-xorg-input-evdev xserver-xorg-input-synaptics xinput usbutils gphoto2 valgrind