p2p/net/swarm: fix racey test

p2p/net/swarm: more connection bugs

this is actually pretty important in case some peers end
up changing addrs, so others dont fail dialing simply for
picking the wrong addr to start with.

This commit introduces a backoff when failing to dial
peers. It makes everything much faster.

feat(repo): FSRepo

* filtering InterfaceListenAddresses(s) instead
* return error if for loops skip
* large dial timeout

@jbenet

The pkg.Interface style is modeled after heap.Interface. Generally, I
find it helpful for interfaces that have many implementations. It
provides clear distinction between the generic interface and the |n|
implementations that implement it (which may be interface types
themselves).

For clients who cannot keep the repo name, one can imagine that the most
likely rename is `ipfsrepo`. In that case, `ipfsrepo.Interface` remains
meaningful.

This is low-pri so it doesn't matter than much. But for the record, the
repo.Interface feels appropriate in this use-case.

@jbenet

@jbenet this removes everything under the path

This may have been failing before.

let me know if this looks off @whyrusleeping @jbenet