reorganize SSH key management

• read the SSH keys only from /etc and not from users home for better auditability. This also makes generating the key lists much easier.
• move deployment of root ssh keys to the ssh role
• improve deployment of user ssh keys in the user role

inventory/ffspveguests

@@ -71,3 +71,4 @@ ffspveguests:
     nrb-backbonetest2.vm.freifunk-stuttgart.de:
       ansible_ssh_host: 2a01:4f8:172:feff:be24:11ff:fe8b:8979
       ansible_ssh_user: root
+    test-ansible01.vm.freifunk-stuttgart.de: