Supports OPERATOR priv level for ipmitool driver

This could be fixed by adding an optional member of node's
driver_info to store the privilege level. And add '-L' option for
ipmitool command call.

Change-Id: Ia3cb2ade8b6823a6d33db2fc22da940211c60b7d
Closes-Bug: #1263790
Merge "Supports OPERATOR priv level for ipmitool driver"