LU-9908 tests: force umount client in test 70e, 41b, and 105

LU-9908 tests: force umount client in test 70e, 41b, and 105

In test_70e, import state may not update while
mds stopping. Since statfs will be invoked in sles12
before umounting, so umount with force flag to avoid
waitting a long time.
Add -f to stopall call in test-framework for the same reason,
to do umount with force flag.

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: I3d1e73b3501e98008ef18c05f7b5498d12cb46fb
Reviewed-on: https://review.whamcloud.com/28767
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>