Improve default logging in valve.py to include datapath.
Improve default logging in valve.py to include datapath.

mwutzke/faucet,Bairdo/faucet,REANNZ/faucet,Bairdo/faucet,shivarammysore/faucet,trungdtbk/faucet,byllyfish/faucet,shivarammysore/faucet,wackerly/faucet,anarkiwi/faucet,mwutzke/faucet,anarkiwi/faucet,faucetsdn/faucet,trentindav/faucet,trentindav/faucet,byllyfish/faucet,REANNZ/faucet,faucetsdn/faucet,gizmoguy/faucet,gizmoguy/faucet,trungdtbk/faucet,wackerly/faucet