Repeated power failures can cause multi echo configuration to connect in single echo mode

If the power input to the hokuyo fails or is flaky, the reconnect logic can incorrectly failover to the single echo mode if the check for multi echo laser fails:

The checks for intensity and multi echo need to more thoroughly parse the return code and throw an exception to trigger the reconnect logic:

https://github.com/ros-drivers/urg_node/blob/indigo-devel/src/urg_c_wrapper.cpp#L435
