(maint) Reword debug message

When puppet autorequired a resource, its debug message used to say:

    Autorequiring File[/Users/josh/.puppet]

Commit b864bfbcd for PUP-3331 added the ability to define autobefore,
autonotify, and autosubscribe relationships, similar to autorequire. In
the process the debug message changed to support these other types of
relationships:

    Forming automation relationship of type <type> with File[/Users/josh/.puppet]

This commit changes the message to be more concise:

    Adding auto<type> relationship with File[/Users/josh/.puppet]
Merge pull request #3409 from joshcooper/maint/master/reword-autorelationship-message

(maint) Reword debug message.