Restructuring/renaming DNS, DHCP, TFTP and netboot installer.

Idea: The role 'dnsmasq' and a new role 'dns-dhcp-tftp' are
drop-in replacements and interchangeable. 'netboot-installer'
works indepently of the role chosen for DNS, DHCP and TFTP.

kerberox.yml

@@ -47,8 +47,8 @@
   roles:
     - up2date-debian
     - two-interface-firewalld
-    - dhcp-dns-dnsmasq
-    - tftp-netboot-installer
+    - netboot-installer
+    - dnsmasq
     - apt-cacher
     - { role: krb5-kdc-ldap, when: not run_in_installer|default(false)|bool }
     - { role: nfs-server, when: not run_in_installer|default(false)|bool }