Use creates parameter instead of unless: test -f

Summary:
2014.7.0 introduced a creates parameter to run only when the
a file doesn't exist.

Reference: https://docs.saltstack.com/en/latest/ref/states/all/salt.states.cmd.html

Test Plan: Check reapply the state is no op

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D973