provisioner/ansible-local: Add support for provisioning with Ansible

post-processors/vagrant: add compression_level option

provisioner/salt-masterless: use communicator.UploadDir

provisioner/salt-masterless: move states to /srv/salt, not /srv/salt/states

[GH-539]

post-processor/vagrant: fix bug in ova support caused by wrong file path

builder/amazon/chroot: use --remove-destination for cp 

contributing: clarify how to submit debug output with a new issue

Delete files at destination before copy. This should help with the dangling
symbolic link issue we've been seeing with ubuntu.

fixes GH-500

fix typo in docs for saltmasterless provisioner. 

website/docs: note shutdown to run as root, why

/cc @mwhooker

provisioner/shell: fix EOF detection

Fixes #507

The scanUnixLine function was erroneously returning empty lines when EOF
was reached.
This commit adds a test for the problem and changes the scanUnixLine
function to elide the trailing \n if no content was read.

Also added a note about shutdown_command that bit me.

post-processor/vagrant: support instance store AMIs [GH-503]

builder/virtualbox: sleep after shutdown before export to avoid session locks

builder/amzon: fix race condition after launching EC2 instance

common/config: config filter function [GH-521]