add fixed-2 cluster
(cherry picked from commit 267aac25acf3ccf34447fc639ff7ca4686bc080c)
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>
(cherry picked from commit f05f90b527b915ca53ae69048a01f6b0adc0cf4b)