Ensure raw_env_vars contains string values only
Ensure raw_env_vars contains string values only

Required to not silently break Ansible runs.
Fixes #658

cimarron-pistoncloud/molecule,metacloud/molecule,cimarron-pistoncloud/molecule,kireledan/molecule,j0lly/molecule,j0lly/molecule,metacloud/molecule,metacloud/molecule,j0lly/molecule,kharkevich/molecule,cimarron-pistoncloud/molecule