Remove old docker packages and other docker upgrade fixes (#2536)

* Remove old docker packages

This removes docker packages that are obsolete if docker-ce packages are to be installed, which fixes some package conflict issues that can occur during upgrades.

* Add support for setting obsoletes=0 when installing docker with yum

roles/docker/tasks/pre-upgrade.yml

@@ -0,0 +1,20 @@
+---
+- name: Ensure old versions of Docker are not installed. | Debian
+  package:
+    name: '{{ item }}'
+    state: absent
+  with_items:
+    - docker
+    - docker-engine
+  when: ansible_os_family == 'Debian' and (docker_versioned_pkg[docker_version | string] | search('docker-ce'))
+
+- name: Ensure old versions of Docker are not installed. | RedHat
+  package:
+    name: '{{ item }}'
+    state: absent
+  with_items:
+    - docker
+    - docker-common
+    - docker-engine
+    - docker-selinux
+  when: ansible_os_family == 'RedHat' and (docker_versioned_pkg[docker_version | string] | search('docker-ce'))