r/base: Clear facts after installing python-selinux

If the Python bindings for SELinux policy management are not installed
when Ansible gathers host facts, no SELinux-related facts will be set.
Thus, any tasks that are conditional based on these facts will not run.
Typically, such tasks are required for SELinux-enabled hosts, but must
not be performed for non-SELinux hosts.  If they are not run when they
should, the deployment may fail or applications may experience issues at
runtime.

To avoid these potential issues, the *base* role now forces Ansible to
gather facts again if it installed the Python SELinux bindings.

Note: one might suggest using `meta: clear_facts` instead of `setup` and
letting Ansible decide if and when to gather facts again. Unfortunately,
this for some reason doesn't work; the `clear_facts` meta task just
causes Ansible to crash with a "shared connection to {host} closed."

roles/base/handlers/main.yml

@@ -0,0 +1,2 @@
+- name: gather facts
+  setup:

roles/base/tasks/main.yml

@@ -10,6 +10,8 @@
   package:
     name: '{{ selinux_python_libs }}'
     state: present
+  notify:
+  - gather facts
   tags:
   - install