builder/digitalocean: send a "shutdown" before snapshotting

Instead of pulling the plug on a droplet with the "poweroff" command,
we first send a soft shutdown to the API, then we poweroff to allow
the snapshot to properly complete.

Sending just a shutdown and then snapshotting wasn't as reliable as
sending the poweroff manually, for reasons unknown to me.

This fixes #332.
Add base support for openstack [GH-155]

This change adds base support for an openstack builder.
Thank you to Rackspace for providing cloud assets to complete this work
and @sam-falvo for working with us on the perigee/gophercloud changes.
website: add openstack page
Add new openstack builder
provisioner/chef-solo: installChef fixed up to use tpl and StartWithUi
provisioner/chef-solo: massive refactor and style nitpick
provisioner/chef-solo: upload cookbooks
Update CHANGELOG
provisioner/chef-solo: remove unused constants and variables
command/build: put build errors in machine readable output
command/build: "end" sentinel in artifact machine-readable output
website: document chef solo provisioner
plugin/provisioner-chef-solo: compile
provisioner/chef-solo: use proper exceute command
command/build: build error machine-readable is targetted to the build
Fix minion config with non tmp dir
Merge pull request #339 from mitchellh/do-soft-shutdown

builder/digitalocean: send a "shutdown" before snapshotting
Update CHANGELOG
Add setting for pillar folder to respect saltstack structure
builder/vmware: ability to not request a PTY for SSH [GH-270]