v.io/x/ref/lib/raft: fix a rare context.CancelFunc leak
v.io/x/ref/lib/raft: fix a rare context.CancelFunc leak

We're fixing leaks of context.CancelFunc closures,
which the spec demands must be called.

This change fixes a rare path in raft.Stop(), which failed to
call the CancelFunc if the raft instance had never been started
after creation.

Change-Id: I1c9e99029cc2007f11f5b42b6ba0bc76cb8d3bea

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