Merge pull request #2583 from edx/benp/upgrade-packer

Upgrade packer so we can use ansible provisioner instead of shell.

playbooks/roles/jenkins_worker/defaults/main.yml

@@ -16,7 +16,7 @@ jenkins_rbenv_root: "{{ jenkins_home }}/.rbenv"
 jenkins_ruby_version: "1.9.3-p374"
 
 # packer direct download URL
-packer_url: "https://dl.bintray.com/mitchellh/packer/0.6.1_linux_amd64.zip"
+packer_url: "https://releases.hashicorp.com/packer/0.8.6/packer_0.8.6_linux_amd64.zip"
 
 # Pip-accel itself and other workarounds that need to be installed with pip
 pip_accel_reqs: