Improved error message and fix within Etc.passwd iterator block

Error message for missing key used to look like this:
Public key from root@web01@web01 not available yet. Skipping

Now looks like this:
Public key from root@web01 not available yet. Skipping

In this line:
 user = pw.name.gsub!(/[^a-zA-Z0-9_]/, '')

If no substitutions were made, user will be set to 'nil'

Not using the gsub_bang method fixes this