(#18468) Further clarify messages in defaults for Debian init scripts. 

The comments explaining the START property in the Debian puppetmaster and puppet init scripts didn't adequately convey that the default settings would prevent the init scripts from starting, but not prevent execution of puppet by other means. Further, the language used was not in alignment with existing documentation (e.g. "puppet client" instead of "puppet agent.")

This changes the comments to note that the puppet master and agent services are prevented from running, not puppet itself, and aligns the language used with existing documentation style.