builder/amazon/chroot:

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

fixes GH-500
contributing: clarify how to submit debug output with a new issue
Merge pull request #545 from mitchellh/contributing-log

contributing: clarify how to submit debug output with a new issue
Merge pull request #544 from mitchellh/fix#500

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