LU-690 test: wait_osc_import_state() fixes

LU-690 test: wait_osc_import_state() fixes

-- increase maxtime to wait the timeout of 1st request;
   take into account at_min value;
-- cleanup wait_osc_import_state() to use _wait_import_state();

Oracle-bug-id: 24498

Signed-off-by: Elena Gryaznova <elena.gryaznova@oracle.com>
Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: I0a3525a02e5ce6ca81082d177df0c5d7d68bea26
Reviewed-by: Vladimir Saveliev <vladimir.saveliev@oracle.com>
Reviewed-on: http://review.whamcloud.com/2496
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>