labs: disable cloud-archive for trusty

Icehouse packages are part of Ubuntu 14.04 LTS (trusty), trying to add
the cloud-archive results in an error. The code is still needed for
precise (Ubuntu 12.04) and presumably for trusty once Juno and later
OpenStack releases become available.

Change-Id: I970f938281f0abfc32a3e0c1467c2dca11dfa676