Fixed TypeError when creating MlnxException

MlnxException expect a 'err_msg' keyword argument.

Change-Id: I4570219c0a6a466391b43cbdaa5372b85566c421
Closes-Bug: #1283990
Signe-off-by: Roey Chen <roeyc@mellanox.com>
Merge "Fixed TypeError when creating MlnxException"