No way to save packer command output

[danshaub]

Before, there was no way to capture the output generated by the packer command, and as such, there was no way to upload the output as an artifact for later use or for logging purposes. This has been solved by the changes in pull request #55

A working version of the workflow with that change active can be found here: https://github.com/marketplace/actions/packer-github-actions-dh_test