Fix typo in unify_hosts script
Description of problem:
In the foreman-rake katello:unify hosts script, there is a simple typo "...please un-unmanage this...".
Version-Release number of selected component (if applicable):
Satellite 6.2.9 Snap 2
Steps to Reproduce:
1. Follow the reproducer steps found in:
Host is registered with subscription-manager but is managed, please un-unmanage this host first.
the text should read "un-manage".