upgrade: run rados python test on bobtail to avoid polluting cluster with pools

Extra pools from test.sh will make this fail:

2013-04-26T11:06:45.631 INFO:teuthology.task.workunit.client.0.err:test_rados.TestRados.test_list_pools ... FAIL
2013-04-26T11:06:45.633 INFO:teuthology.task.workunit.client.0.err:
2013-04-26T11:06:45.633 INFO:teuthology.task.workunit.client.0.err:======================================================================
2013-04-26T11:06:45.633 INFO:teuthology.task.workunit.client.0.err:FAIL: test_rados.TestRados.test_list_pools
2013-04-26T11:06:45.634 INFO:teuthology.task.workunit.client.0.err:----------------------------------------------------------------------
2013-04-26T11:06:45.634 INFO:teuthology.task.workunit.client.0.err:Traceback (most recent call last):
2013-04-26T11:06:45.634 INFO:teuthology.task.workunit.client.0.err:  File "/usr/lib/python2.7/dist-packages/nose/case.py", line 197, in runTest
2013-04-26T11:06:45.634 INFO:teuthology.task.workunit.client.0.err:    self.test(*self.arg)
2013-04-26T11:06:45.634 INFO:teuthology.task.workunit.client.0.err:  File "/home/ubuntu/cephtest/1527/mnt.0/client.0/tmp/test_rados.py", line 37, in test_list_pools
2013-04-26T11:06:45.634 INFO:teuthology.task.workunit.client.0.err:    eq(set(), self.list_non_default_pools())
2013-04-26T11:06:45.635 INFO:teuthology.task.workunit.client.0.err:  File "/usr/lib/python2.7/dist-packages/nose/tools.py", line 31, in eq_
2013-04-26T11:06:45.635 INFO:teuthology.task.workunit.client.0.err:    assert a == b, msg or "%r != %r" % (a, b)
2013-04-26T11:06:45.635 INFO:teuthology.task.workunit.client.0.err:AssertionError: set([]) != set(['foo.24250.', 'test-rados-api-plana05-22578-27', 'foo.24250', 'foo.23821'])