Fix requisite for hostname

Summary:
after_hostname_change and after_hostname_change_debian
depends of a file state with "/etc/hostname" id.

This is a follow-up for b88a308fec2d.

Test Plan: Ensure after_hostname_change is triggered

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1271