LU-2194 test: avoid wrong eviction in recovery_small

LU-2194 test: avoid wrong eviction in recovery_small

in subtest 19a and 19b of recovery_small, the locks from OST/MDT
should be cancelled before "drop_ldlm_cancel" to avoid wrong eviction
from OST/MDT for it will also drop its lock cancellation request.

Change-Id: I49d1d189f6791224a3f132dc8cf2dd8b3d51d43e
Signed-off-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-on: http://review.whamcloud.com/5679
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Hudson
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>