Add "Conflicts" to our lxc-docker package to make it more clear that we can't/shouldn't be installed alongside either "docker" or "docker.io"

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

hack/make/ubuntu

@@ -119,6 +119,8 @@ EOF
 		    --deb-recommends xz-utils \
 		    --description "$PACKAGE_DESCRIPTION" \
 		    --maintainer "$PACKAGE_MAINTAINER" \
+		    --conflicts docker \
+		    --conflicts docker.io \
 		    --conflicts lxc-docker-virtual-package \
 		    --provides lxc-docker \
 		    --provides lxc-docker-virtual-package \