nuke: bring stale kernel client handling back
nuke: bring stale kernel client handling back

Commit 1d47a121b385 ("Fix nuke, redo some cleanup functions") broke
stale kernel client map/mount handling by dropping reboot arguments.
While for kcephfs we can use 'umount -f' to avoid sync (it used to not
work, but is mostly fixed now, I believe), currently there is nothing
we can do for a local filesystem mounted on top of krbd.

Signed-off-by: Ilya Dryomov <152d4c5bebf13a5b809d42b4d789cf9d887e6698@gmail.com>

SUSE/teuthology,SUSE/teuthology,dmick/teuthology,ktdreyer/teuthology,ceph/teuthology,ktdreyer/teuthology,dmick/teuthology,dmick/teuthology,ceph/teuthology,SUSE/teuthology