Use Opscode Omnibus installer for Chef

All official Digital Ocean images should be supported by it.

At least Debian might not have curl in the base image, so use wget for all.
Add ca_path config variable to allow users to specify the certificate file on OSX
Fix error in Create#terminate
Remove debugging printout
Merge pull request #13 from rjsamson/osx_certificates

Add ca_path config variable to allow users on other platforms (OSX) to configure SSL properly.
Merge pull request #12 from tmatilai/chef-omnibus-installer

Use Opscode Omnibus installer for Chef