Update with_items loops to use new-ish "loop" keyword

Ansible 2.4 and 2.5 are moving away from specialized loop functions
and the old syntax will eventually be deprecated and removed. I did
not change the with_fileglob loops because I'm not sure about their
syntax yet.

See: https://docs.ansible.com/ansible/latest/user_guide/playbooks_loops.html

roles/common/tasks/sshd.yml

@@ -15,7 +15,7 @@
 
 - name: Remove DSA and ECDSA host keys
   file: name=/etc/ssh/{{ item }} state=absent
-  with_items:
+  loop:
     - ssh_host_dsa_key
     - ssh_host_dsa_key.pub
     - ssh_host_ecdsa_key