Provides the following options for injection:

:inject_packages: an rpm path or list of rpm paths which will be
                  copied and installed on instance.
:inject_archives: an archive or list of archives which will
                  be copied and extracted on instance.
:inject_files: a file path or list of file paths which
               will be copied to instance.
:execute: a command or list of commands to run.
:install: a package name or list of package names to
         install from an existing repo.

The injection happens in that order.