Packer was using the original file reader when uploading, instead of the UnixReader /cc @mitchellh

/cc @mwhooker - I changed the interface up a bit to return an error,
since things should return errors in Go (the ui.Error bit was kind of
ghetto because it had no way to bubble that error up except through the
UI).

Using this, I made it so that the communicator uses both a
CommandWrapper and ShellCommand with chroot so that the chroot commannd
is also wrapped (it wasn't before).

I think the functionality of all this is the same but I'd love if you
could look it over and make sure.

/cc @mwhooker

build/amazon/chroot: command_wrapper to support sudo-less

builder/digitalocean: error message key is "message" not "error_message"

provisioner/chef-solo: fix .RolesPath and .DataBagsPath in the config template

scripts: build.sh exits without being killed by SIGTERM

website: removing the docs for digital ocean's optional param 'event_delay'

This reverts commit 73c5aec24d0a504ecfbae038b4b7effb54adb929.

Conflicts:
	builder/amazon/chroot/step_copy_files.go