LU-951 test: waiting import state in fail().

LU-951 test: waiting import state in fail().

Anyway, There still has a rare chance that the request meet
a invalid import after fail() return. So we should waiting
import restore to a certain state and doing next operation.
Add wait_import_state_mount() to check import state while
client has a mount point.

Signed-off-by: yang sheng <yang.sheng@intel.com>
Change-Id: I55ccb0fd30d69eae651978804ef1e303d9939a71
Reviewed-on: http://review.whamcloud.com/5531
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>