ARM64 and PPC64 testing is diabled

[Curtis Hovey-Canonical]

The lab gateway is still down for maintenance (I assume). I disabled
the arm64 and ppc64 tests so that they juju is not blamed for a
failure.

I wasn't expecting loss of access because of maintenance to batuan
because CI uses a alternate route into the lab.

-- 
Curtis Hovey
Canonical Cloud Development and Operations
http://launchpad.net/~sinzui