veyron/tools/mgmt/device: rename node->device, cl 4 of N (go/vissue/496)
veyron/tools/mgmt/device: rename node->device, cl 4 of N (go/vissue/496)

Update device cmd-line tool doc.

Change-Id: Ib68029681c5999248d006ee4f9ae80689f1c19bc

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref