Fixed regression with AmazonLinux Docker install, increased coverage of

testing Docker installation as Fedora was missing python-dnf dependency.

.travis.yml

@@ -21,9 +21,13 @@ env:
     # Test installing docker
     - MOLECULE_DISTRO: geerlingguy/docker-centos7-ansible:latest
       MOLECULE_PLAYBOOK: playbook-docker.yml
+    - MOLECULE_DISTRO: geerlingguy/docker-ubuntu1804-ansible:latest
+      MOLECULE_PLAYBOOK: playbook-docker.yml
+    - MOLECULE_DISTRO: geerlingguy/docker-amazonlinux2-ansible:latest
+      MOLECULE_PLAYBOOK: playbook-docker.yml
 
     # Test using alternate port and using wireguard as the flannel backend
-    - MOLECULE_DISTRO: geerlingguy/docker-fedora30-ansible:latest
+    - MOLECULE_DISTRO: geerlingguy/docker-fedora31-ansible:latest
       MOLECULE_PLAYBOOK: playbook-docker-altport-wireguard.yml
 
     # Test disabling all deployments

tasks/install-docker-amazon.yml

@@ -0,0 +1,10 @@
+---
+
+- name: Ensure docker is installed using amazon-linux-extras
+  command: amazon-linux-extras install docker
+  args:
+    creates: /etc/docker
+  notify:
+    - restart docker
+
+- meta: flush_handlers

tasks/install-docker-prerequisites-redhat.yml

@@ -1,5 +1,15 @@
 ---
 
+- name: Ensure python-dnf is installed
+  package:
+    name: "{{ 'python-dnf' if ansible_python_version is version_compare('3.0.0', '<') else 'python3-dnf' }}"
+    state: present
+  register: ensure_python_dnf_installed
+  until: ensure_python_dnf_installed is succeeded
+  retries: 3
+  delay: 10
+  when: ansible_pkg_mgr == 'dnf'
+
 - name: Ensure Docker prerequisites are installed
   yum:
     name: