add fixed-2 cluster
rados: use 2 instead of 3 machines

Put the client on the same node as some of the osds.  This shouldn't cause
any problems.  It will make timing a bit different, but if anything that
is probably a good thing.

Signed-off-by: Sage Weil <sage@inktank.com>
rgw: use 2 node cluster

Signed-off-by: Sage Weil <sage@inktank.com>
rbd: use 2 node cluster, mostly.

Not for the collection that includes KVM tests.

Signed-off-by: Sage Weil <sage@inktank.com>