Add pxp-agent log rotation for Solaris 10 and 11

It looks like /etc/logadm.conf entries can be managed via `logadm` commands.

To add an /etc/logadm.conf entry:

logadm -w /var/log/puppetlabs/pxp-agent/pxp-agent.log -C 30 -p 1d -a 'pkill -USR2 pxp-agent; true'

To remove an /etc/logadm.conf entry:

logadm -r /var/log/puppetlabs/pxp-agent/pxp-agent.log

There may be some prerequisite Vanagon work needed for this.