make: turn ubuntu docker into template stable

make: turn ubuntu docker into template

This allows us to easily add more ubuntu docker targets (which following
patches will do).

Also, we no longer need the mkdir command.

--- a/.hgignore	Wed Apr 27 14:02:18 2016 -0700
+++ b/.hgignore	Tue Apr 26 23:33:17 2016 -0700
@@ -30,6 +30,7 @@
 contrib/chg/chg
 contrib/hgsh/hgsh
 contrib/vagrant/.vagrant
+contrib/docker/ubuntu-*
 dist
 packages
 doc/common.txt

--- a/Makefile	Wed Apr 27 14:02:18 2016 -0700
+++ b/Makefile	Tue Apr 26 23:33:17 2016 -0700
@@ -181,8 +181,10 @@
 	mkdir -p packages/debian-jessie
 	contrib/dockerdeb debian jessie
 
-docker-ubuntu-trusty:
-	mkdir -p packages/ubuntu-trusty
+contrib/docker/ubuntu-%: contrib/docker/ubuntu.template
+	sed "s/__CODENAME__/$*/" $< > $@
+
+docker-ubuntu-trusty: contrib/docker/ubuntu-trusty
 	contrib/dockerdeb ubuntu trusty
 
 fedora20:

--- a/contrib/docker/ubuntu-trusty	Wed Apr 27 14:02:18 2016 -0700
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,11 +0,0 @@
-FROM ubuntu:trusty
-RUN apt-get update && apt-get install -y \
-  build-essential \
-  debhelper \
-  dh-python \
-  devscripts \
-  python \
-  python-all-dev \
-  python-docutils \
-  zip \
-  unzip

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/docker/ubuntu.template	Tue Apr 26 23:33:17 2016 -0700
@@ -0,0 +1,11 @@
+FROM ubuntu:__CODENAME__
+RUN apt-get update && apt-get install -y \
+  build-essential \
+  debhelper \
+  dh-python \
+  devscripts \
+  python \
+  python-all-dev \
+  python-docutils \
+  zip \
+  unzip