ceph_manager: don't mark out an out osd on kill_osd(..., mark_out=True)

ceph_manager: don't mark out an out osd on kill_osd(..., mark_out=True)

Fixes

2013-07-27T02:02:23.879 INFO:teuthology.task.thrashosds.thrasher:Recovered, killing an osd
2013-07-27T02:02:23.879 INFO:teuthology.task.thrashosds.thrasher:Killing osd 2, live_osds are [3, 4, 0, 1, 5, 2]
2013-07-27T02:02:24.547 INFO:teuthology.task.thrashosds.thrasher:Removing osd 2, in_osds are: [4, 0, 1, 5]
...
ValueError: list.remove(x): x not in list

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