r/squid: Fix SELinux AVC denial after cache init

Running `squid -z` as *root* leaves behind temporary files in
`/dev/shm`.  When *squid.service* starts squid, in the proper SELinux
domain, it is unable to access these files and crashes.  To avoid this,
we mount a private *tmpfs* so no existing files are accessible in the
service's namespace.

roles/squid/handlers/main.yml

@@ -1,3 +1,7 @@
+- name: reload systemd
+  systemd:
+    daemon_reload: true
+
 - name: initialize squid cache directories
   command:
     /usr/sbin/squid -N -z -F -f /etc/squid/squid.conf