AIX user provider changes gecos field on every run if comment is ''

if you define the following test class

user

{ 'aixtest': comment => '', }

puppet is going to change the geocs (comment) field on every run, executing `chuser gecos= aixtest`.
this happens because

lsuser -c aixtest

does not include the gecos field if it is empty. just change the class to

user

{ 'aixtest': comment => 'aixtest', }

and it only gets changed once, as `lsuser -c aixtest` now reports the gecos field.

thanks
toni