cmd/gnmi: Add 'clog' debug option
cmd/gnmi: Add 'clog' debug option

The clog option will start a subscription and then never read any of
the results. This can cause buffering and coalescing load on gNMI
server implementations.

Change-Id: Ibc0844190022b74eae4f998f0865e65f391d001b

aristanetworks/goarista,aristanetworks/goarista