Use new token allocation for non bootstrap case as well.

There are couple reasons I think we should use the new token allocation for non bootstrap case as well.

1. In some cases, We want to bring up nodes, but do not need to stream any data to the new nodes. So we want to allocate correct tokens, and skip the JOIN state, which should avoid triggering pending range calculation on other nodes as well. On use case is when we bring up a new DC.

2. We can unify the token allocation code path for both bootstrap and non-bootstrap use case.