Add handler flushing to roles that need it

This patch adds handler flushing as the last task in each role to ensure
that there are log files present when the rsyslog client configuration
task is executed a little later in the playbook that consumes the role.

Closes-Bug: #1458822
Change-Id: I92a26b620aa7bc0fbe33175594d37da7d5aca7df

tasks/main.yml

@@ -38,3 +38,5 @@
   tags:
     - nova-compute
 
+- name: Flush handlers
+  meta: flush_handlers