Refactor docker playbook

- Removed copyright notice
- Variablize 'hosts' value in the playbook
- Install Jenkins agent before running Docker role

docker.yml

@@ -1,21 +1,7 @@
-# Copyright (C) 2020  Kris Lamoureux
-#
-# This program is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, version 3 of the License.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <https://www.gnu.org/licenses/>.
-
 - name: Install Docker Server
-  hosts: dockerhosts
+  hosts: "{{ PLAYBOOK_HOST | default('none') }}"
   become: true
   roles:
     - base
-    - docker
     - jenkins
+    - docker