(PUP-1510) Fixed forcelocal bug with ensure => absent

The forcelocal option was referencing a command that was not
previously defined which was throwing an exception.  The forcelocal
feature does not need to use a special command to delete local users,
only to add them.  So the special logic for delete was removed and
forcelocal now uses userdel to ensure absent on a user.
Merge pull request #2354 from jjulien/pup1510

(PUP-1510) Fixed forcelocal bug with ensure => absent
Merge branch 'master' of https://github.com/puppetlabs/puppet