.gitignore: generated packer_cache directory

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
.gitignore: generated .box files

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
virtualbox.json: use the virtualbox type so as to get guest additions

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Run "fix" against latest packer

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
update the target descriptors with recent snapshot versions

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
.gitignore: some temporary directories created by packer

Signed-off-by: Gregory M. Turner <gmt@be-evil.net>
Merge pull request #4 from gmt/master

Misc minor improvements and updates