openflow_topology: fix xid_generator
nicira.py: add nx_reg_move
nicira.py add nx_output_reg
Merge pull request #53 from sstjohn/for-murphy

PR: Add nx output_reg and reg_move; topo fix

Primarily, this adds nx_reg_move and nx_output_reg actions.
Secondarily, it fixes a misnamed variable in the OpenFlowSwitch topology class.