CentOS: Increase timeout for "yum update -y"

Currently we observe that the yum_update resource sometimes fail in
gate because of timeout. Let's increase the timout from the default
300 seconds to the doubled one, 600 seconds since the task tends
to take some time.

Change-Id: Ic004bccee196d97301d3bf1512fdef978af670ed

manifests/repo/redhat/redhat.pp

@@ -231,6 +231,7 @@ class openstack_extras::repo::redhat::redhat(
     exec { 'yum_update':
       command     => "/usr/bin/${yum_command} update -y",
       refreshonly => true,
+      timeout     => 600,
     }
     Exec['yum_refresh'] ~> Exec['yum_update'] -> Package <||>
   }