Quick UX feedback for pnet

This is an issue to gather feedback for @Kubuxu on the pnet demo, and implementation.

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1. Daemon output should show that it's using a key.
- something like `Private network: shared-key `
- or something like `Private network: shared-key `
- or at least something like: `Private network: shared-key `
2. Print out errors or warnings when a connection is attempted that fails.
- would be nice to get a sense of how many connections are attempted with wrong keys
- helps you notice you have the wrong bootstrap nodes on (if you dial out)
- helps you notice incoming dials from others
- helps you notice _why_ your friend cannot connect to you
3. may be useful to have a tool like `ipfs-key-gen` or `libp2p-key-gen` that is able to
make the keys. (and mount this in `ipfs` at `ipfs swarm key` or something).