orchestra: disable re-keying to fix Key-exchange timed out

orchestra: disable re-keying to fix Key-exchange timed out

Disable re-keying entirely: it does not work at all and alway times
out. Here is the reproducer:

ceph-workbench ceph-qa-suite --verbose --suite upgrade/infernalis-x --suite-branch jewel --ceph jewel --ceph-git-url https://github.com/ceph/ceph --filter 'upgrade:infernalis-x/stress-split/{0-cluster/start.yaml 1-infernalis-install/infernalis.yaml 2-partial-upgrade/firsthalf.yaml 3-thrash/default.yaml 4-mon/mona.yaml 5-workload/{rbd-cls.yaml rbd-import-export.yaml readwrite.yaml snaps-few-objects.yaml} 6-next-mon/monb.yaml 7-workload/{radosbench.yaml rbd_api.yaml} 8-next-mon/monc.yaml 9-workload/{rbd-python.yaml rgw-swift.yaml snaps-many-objects.yaml} distros/centos_7.2.yaml}'

Which always fails after ~4h with the following:

2016-03-17T23:44:32.607 INFO:tasks.thrashosds.thrasher:Traceback (most recent call last):
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 639, in wrapper
    return func(self)
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 693, in do_thrash
    self.choose_action()()
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 445, in fix_pgp_num
    self.ceph_manager.set_pool_pgpnum(pool)
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 1294, in set_pool_pgpnum
    if self.get_num_creating() > 0:
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 1456, in get_num_creating
    pgs = self.get_pg_stats()
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 1325, in get_pg_stats
    out = self.raw_cluster_cmd('pg', 'dump', '--format=json')
  File "/home/ubuntu/src/ceph-qa-suite_master/tasks/ceph_manager.py", line 810, in raw_cluster_cmd
    stdout=StringIO(),
  File "/home/ubuntu/teuthology/teuthology/orchestra/remote.py", line 196, in run
    r = self._runner(client=self.ssh, name=self.shortname, **kwargs)
  File "/home/ubuntu/teuthology/teuthology/orchestra/run.py", line 378, in run
    r.wait()
  File "/home/ubuntu/teuthology/teuthology/orchestra/run.py", line 94, in wait
    greenlet.get()
  File "/home/ubuntu/teuthology/virtualenv/local/lib/python2.7/site-packages/gevent/greenlet.py", line 274, in get
    raise self._exception
SSHException: Key-exchange timed out waiting for key negotiation

http://tracker.ceph.com/issues/15236 Fixes: #15236

Signed-off-by: Loic Dachary <loic@dachary.org>