Don't clean after `yum update` in script
Don't clean after `yum update` in script

There's no need to clean after the yum update call since we're running
all `yum` commands in the same script. Run a single `yum clean all`
command at the end of the install process.

Change-Id: Ifcb686b346cada5fb5398a26819479231d7e8812

openstack/tripleo-common,openstack/tripleo-common