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

[chadrockey]

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