(#5108) Update service type docs for new hasstatus default

Commit #7d35a479 changed the default value of the service type's hasstatus
attribute. This was never documented. This commit documents the changed
behavior, which will end up in the type references (and puppet describe) for
version 2.7.2 and greater. (I intend to manually change the cached references
for versions 2.7.[01].)