Fixes #228 (Adds ability to remove active_model bound to a node)

This pull request adds ability to remove the active_model instance that is bound to a specific node, based on the hardware_id (SMBIOS UUID) or the Hanlon-assigned UUID of the node that active_model instance is bound to. Also adds the ability to get a specific active_model instance based on those same two values (either the hardware_id or the Hanlon-assigned UUID of the node that active_model instance is bound to; previously only a search by hardware_id of the bound node was supported).