LU-2280 tests: wait osc import to be FULL after sanityn 34.

1. It should wait osc import to be FULL before proceeding to the
following test.

2. fixes in osc_wait_import_event for waiting multiple osc imports.

Signed-off-by: Wang Di <di.wang@intel.com>
Change-Id: Ia054264954a6e0aacadc7c8062c2f353cd87f834
Reviewed-on: http://review.whamcloud.com/4468
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>