diamond: Let diamond read the puppet state file

Currently, /var/lib/puppet is set to have no permissions for o,
causing diamond to not be able to read the last_run_summary.yaml
file despite that file having appropriate permissions set by
puppet.

So instead, we let diamond sudo to puppet just to be able to
read that particular file, via cat.

Change-Id: I615963917a5a042e645b2caec441369149a9ea8a