LU-15653 client: able to cleanup devices manually

LU-15653 client: able to cleanup devices manually

Using 'lctl cleanup/detach' could be needed in situations
with unclean umount. Meanwhile that doesn't work now for
LMV and also could cause panic after all

Patch restores ability to cleanup/detach client devices
manually.
- debugfs and lprocfs cleanup in lmv_precleanup() are moved
  lmv_cleanup() to be not cleared too early. This prevents
  hang on 'lctl cleanup' for LMV device
- test 172 is added in sanity. It skips device cleanup during
  normal umount, keeping device alive without client mount
  then manually cleanups/detaches them
- prevent negative lov_connections in lov_disconnect() and
  handle it gracefully
- remove obd_cleanup_client_import() in mdc_precleanup(),
  it is called already inside osc_precleanup_common()

Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I8a3868fabd1d805e827d04852d1614a3fe57ce35
Reviewed-on: https://review.whamcloud.com/46859
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>