Add back the mistakenly removed "ceph osd set noscrub/nodeep-scrub"

Fixes: #5868
Signed-off-by: Dan Mick <dan.mick@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
mon/MonCommands: fix typo nobackfile -> nobackfill

Signed-off-by: Sage Weil <sage@inktank.com>
qa/workunits/cephtool/test.sh: test set/unset of all osd flags

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