Fixes bug in error handling code from previous pull request

This is a quick PR to fix a bug that I just detected in PR #207 (which was just merged)...this fixes a bug that only shows up when you try to access the newly added BMC-related functionality from a machine that doesn't have a BMC; in those cases, an error is thrown because the RESTful interface is trying to access the node_uuid value instead of the node.uuid value...will merge shortly