Set master hostname in puppet.conf during install

Adds another ini_setting resource to create an [agent] block in
/etc/puppet/puppet.conf and set the puppet master hostname to the
current hostname.  This will only be activated on build-server roles
and the all_in_one scenario.  Without this it's necessary to specify
the puppet master hostname each time puppet agent is run.

Change-Id: Ic6832ebec44e198e26b3b3553b315ead8e93feb5
Closes-Bug: 1285307
Merge "Set master hostname in puppet.conf during install"