Bad initial connection disables intensity publishing

[mferenduros]

If our robots power on a laser after first starting urg_node, the first connection attempt sometimes fails with persistent checksum errors.
This causes the driver to fail the IsIntensitySupported() test, which permanently clears the publish_intensity_ flag.

After repeated checksum errors the driver will reset and connect successfully but publish_intensity_ will be clear so we will not receive intensity info.
The same logic appears to apply to multiecho, but we don't have a multiecho device to test with.

We're using #58 which appears to fix the issue.