VirtualBox script changed to convert image untouched

With config drive there is no need to crack image to insert SSH keys. Then VirtualBox script was changed to just download CoreOS image and convert it to VDI format.
Script to create basic config-drive

New script that creates a basic config-drive, ideal to testing purpose.
cleanup: remove a couple references to chrome-bot
cleanup: remove source location migration code

This code is not applicable to us, it predates CoreOS and is a weird
thing for common.sh to be doing as well. Instead always define
CHROOT_TRUNK_DIR to /mnt/host/source, create ~/trunk in make_chroot.
make_chroot: remove unneeded modifications

These are assorted tweaks that are already setup in the tarball.
Merge pull request #331 from marineam/cleanup

Misc cleanup
Merge pull request #239 from skarllot/master

Changes to VirtualBox convert script
Hyper-V & Azure build support

Add Hyper-V and Azure as build targets for development images.
Merge pull request #332 from szarkos/hv_azure-build

Initial Hyper-V & Azure build support
vm_image_util: use new azure and hyperv oem packages
Merge pull request #333 from marineam/oem

vm_image_util: use new azure and hyperv oem packages
Added --oem_pkg oem override option to image_to_vm.sh

This sets the IMG_FORCE_OEM_PACKAGE variable to the supplied string.  If a
':' is present, what follows it gets put in the IMG_FORCE_OEM_USE variable
and what precedes in the former.

_get_vm_opt() has been modified to generally support forced overrides such
as this one, simply set variables named IMG_FORCE_$opt.

Now you can do things like:

for fmt in cloudstack \
		digitalocean \
		ec2-compat:ec2 \
		ec2-compat:openstack \
		ec2-compat:brightbox \
		exoscale \
		gce \
		hyperv \
		rackspace \
		rackspace-onmetal; do
	./image_to_vm.sh --format=qemu --oem_pkg=$fmt
	../build/images/amd64-usr/latest/coreos_developer_qemu.sh -curses
done

rather than having to modify build_library/vm_image_util.sh to test oem
builds in qemu.
Merge pull request #334 from vcaputo/i2v_def_oem_arg

Added --oem_pkg option to image_to_vm.sh
prod_image_util: clean up /etc cleanup code

Pruning files via INSTALL_MASK in the profile is a bit more apropriate
since it allows us to keep most of that info in one place. The only
parts that need to be deleted or adjusted here are inputs and outputs of
`env-update` which has to be run after everything is installed.

Previously we didn't actually clean up `env.d` at all which lead at
least one user to think they should edit those files and run
`env-update` themselves but we don't ship that tool on prod images.
Merge pull request #335 from marineam/etc

prod_image_util: clean up /etc cleanup code
ALEX: fix sizing and add kernel params