Use Jinja to manage includes

The drawback to the native `%include` Kickstart directive is that it
requires a static, hard-coded, absolute path.  This means that we
cannot, for example, host a copy of the kickstarts from a different
branch for testing, without modifying the URLs of all the included
files.

Switching to using Jinja templates introduces a build step, but the
result is that the artifacts are self-contained.  This way, they can be
deployed anywhere.  I'm not sure where I'll put them, though, and
they'll need a Jenkins job to run the build and publish them.

fedora-rpi.ks.j2

@@ -0,0 +1,5 @@
+{# vim: set ft=sh.jinja : -#}
+ignoredisk --only-use /dev/mmcblk0
+{% include "fedora-disk-dch.ks" %}
+{% include "fedora-rpi-common.ks.j2" %}
+{% include "autoprovision.ks" %}