Only update packages indexes if the cache is 1 hour old

I have added cache_valid_time=3600 for the first task in each
tag that could be possibly running apt-related commands. For ex,
the "nginx" tag is also in the "packages" tag, but sometimes you
run the nginx tag by itself (perhaps repeatadely), so you'd want
to limit the update unless the cache was 1 hour old

roles/common/tasks/packages_Ubuntu.yml

@@ -7,7 +7,7 @@
   when: ansible_distribution_version == '14.04'
 
 - name: Upgrade base OS
-  apt: upgrade=dist update_cache=yes
+  apt: upgrade=dist update_cache=yes cache_valid_time=3600
 
 - name: Install base packages
   apt: pkg={{ item }}