Add exec.d support for private cloud pre-install customization
add interface for subordinate charm to provide image modification scripts
Merge pull request #19 from mikemccracken/add-image-modifier-hook

add interface for subordinate charm to provide image modification scripts
Merge pull request #17 from mikemccracken/add-execd

Add exec.d support for private cloud pre-install customization
add name_prefix config item to GlanceMirror call
add content_id_template config