Upgrade on AIX nodes does not trigger 2nd puppet run and start agent

Original ticket description:

Basic Info
Module Version: 4.1.1
Puppet Version: upgrading from 6.16 to 6.17
OS Name/Version: Reproduced on AIX 7.2 but customer has said it affects all AIX

Desired Behavior:

From the pull request the expected behaviour:

The newly added resource attempts to figure out if a Puppet upgrade
was performed, then stops the run altogether. If Puppet is being run
as a service, the HUP signal will have the daemon trigger a subsequent
Puppet run that will evaluate the remaining resources.

Actual Behavior:

When upgrading and leaving puppet to run as a service the 2nd run does not happen and the puppet service and pxp-agent are left offline making a manual puppet run required. 

The customer who reported the issue has 250 nodes on AIX.

Updated ticket description:

This is a regression in puppet-agent caused by PUP-3721, originally fixed in PA-390.