Add support for routing all storage operations through raft.

The tests pass with this change most of the time but there are some
timing issues around the initial election and tests using IsTrueWithin,
so everything still uses noopRaft until that can be fixed.

@spencerkimball @cockroachdb/developers 
this looks fishy. Couldn't the localRPCTransport just bail on any Accept() error and omit this bit?