Don't install from untested raspberry-pi repo

We only want released firmware in our image.
Add working directories to .gitignore
Don't install copy of Oracle license

We're not installing Oracle Java in our images, so there's no need to
add the license.
Set hostname to localhost.

This is necessary to enable setting the hostname from dhcp.
Don't add startx notice to motd

Our image won't have X, so this is unnecessary
Reduce stage3 package list.

Removing packages that aren't needed for a minimal install.
Remove NOOBS stuff.

We're not going to be using NOOBS
Remove tweaks to default .bashrc

Prefer to stick with the stock debian one.  Tweaks can be done later by
a config management tool, and shouldn't be part of the base image
Fix network subnet in qemu image.

It was defaulting to a class A subnet, which let to conflicts with other
10.* addresses in the host network.
Update debian and raspbian mirrors.

Use the mirrordirectors for both to always get a nearby mirror
Add support for an apt proxy.

If set, this gets used for bootstrapping the image, and also configured
inside the image for future package installs.
Don't install raspi-config

Unneeded - we can do all this config without it.
Remove unused/redundant script sections
Reduce image size

We're only creating a minimal install, so it doean't need to be as big
as for a full image.
Configure timezone in stage2

Setting timezone values in debconf in stage3 is no good because tzdata
is already installed by then, therefore the changes don't take effect.
Fix sudo in image export

Because attach_image_to_nbd calls sudo in the background, this can lead
to mixed up output when prompting for passwords.  Calling sudo -v
beforehand prevents this.
Update rpi-issue to reference forked repo.
Use DEBIAN_FRONTEND=noninteractive

Prevents errors about loading up other interactive frontends
Install stage3 packages in one batch.

Much quicker this way as it only has to resolve dependencies once.
Allow hostname to be set from dhcp.

Requires workaround for dhcp client scripts. See
http://blog.schlomo.schapiro.org/2013/11/setting-hostname-from-dhcp-in-debian.html
for more details.