[Kbucket] Better address management for candidate peers

[aarshkshah1992]

Disassociating Routing Table membership from connectivity is done as part of libp2p/go-libp2p-kbucket#50.

However, we might not have the address for a disconnected candidate when we want to dial it because it might have been evicted by the peer store as documented in the "Address managament" section of this comment.

We need to fix this after #800 goes in and the Routing table OR the DHT has a way to signal the peerstore to keep an address around till we need it.