MRP-1671 ldlm: some fixes for mrp-395/mrp-1366

- do not detach all blocked locks from export when canceling just 1
  lock; otherwise locks will be cancelled much later;
- do not remove lock from waiting list on AST error before moving
  it to elt_expired_locks list, because it removes it from export
  list too; otherwise this blocked lock will not be cancelled
  immediately on failed export;
- cancel lock instead of just destroy for failed export, to make
  full cleanup, i.e. remove it from export list.

Signed-off-by: Vitaly Fertman <vitaly_fertman@xyratex.com>
Change-Id: I38a0b651450d873e59335a01cc7eea081324073e
Reviewed-on: http://morpheus.xyus.xyratex.com:8443/gerrit/1549
Reviewed-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Tested-by: Jenkins
Tested-by: Elena Gryaznova <Elena_Gryaznova@xyratex.com>
Reviewed-by: Alexey Lyashkov <Alexey_Lyashkov@xyratex.com>
Reviewed-by: Vitaly Fertman <Vitaly_Fertman@xyratex.com>