Remove update_cache for yum

This patch removes the update_cache step when installing RabbitMQ
with yum. Updating the cache forcefully isn't required after changing
locked versions or changing repo priorities.

Change-Id: I089695069bb4c12844df9d3dd9f72a7503d38cdd
(cherry picked from commit 68c754f692)

tasks/install_yum.yml

@@ -71,7 +71,6 @@
   yum:
     pkg: "{{ item }}"
     state: "{{ rabbitmq_package_state }}"
-    update_cache: yes
   register: install_packages
   until: install_packages|success
   retries: 5