In order to improve the operator experience we want the node to dial
seeds immediately if there are no peers to connect to. Until now the
routine responsible for ensuring peers are connected to would wait
a random amount of time up to 30s (if not configured otherwise).

* expose AuthEnc in the P2P config

if AuthEnc is true, dialed peers must have a node ID in the address and
it must match the persistent pubkey from the secret handshake.

Refs #1157

* fixes after my own review

* fix docs

* fix build failure

```
p2p/pex/pex_reactor_test.go:288:88: cannot use seed.NodeInfo().NetAddress() (type *p2p.NetAddress) as type string in array or slice literal
```

* p2p: introduce peerConn to simplify peer creation

* Introduce `peerConn` containing the known fields of `peer`
* `peer` only created in `sw.addPeer` once handshake is complete and NodeInfo is checked
* Eliminates some mutable variables and makes the code flow better
* Simplifies the `newXxxPeer` funcs
* Use ID instead of PubKey where possible.
        * SetPubKeyFilter -> SetIDFilter
        * nodeInfo.Validate takes ID
        * remove peer.PubKey()

* persistent node ids

* fixes from review

* test: use ip_plus_id.sh more

* fix invalid memory panic during fast_sync test

```
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: panic: runtime error: invalid memory address or nil pointer dereference
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x98dd3e]
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]:
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: goroutine 3432 [running]:
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.newOutboundPeerConn(0xc423fd1380, 0xc420933e00, 0x1, 0x1239a60, 0
xc420128c40, 0x2, 0x42caf6, 0xc42001f300, 0xc422831d98, 0xc4227951c0, ...)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/peer.go:123 +0x31e
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.(*Switch).addOutboundPeerWithConfig(0xc4200ad040, 0xc423fd1380, 0
xc420933e00, 0xc423f48801, 0x28, 0x2)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:455 +0x12b
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.(*Switch).DialPeerWithAddress(0xc4200ad040, 0xc423fd1380, 0x1, 0x
0, 0x0)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:371 +0xdc
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: github.com/tendermint/tendermint/p2p.(*Switch).reconnectToPeer(0xc4200ad040, 0x123e000, 0xc42007bb00)
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:290 +0x25f
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: created by github.com/tendermint/tendermint/p2p.(*Switch).StopPeerForError
2018-02-21T06:30:05Z box887.localdomain docker/local_testnet_4[14907]: #011/go/src/github.com/tendermint/tendermint/p2p/switch.go:256 +0x1b7
```

1. remove pointer
2. add Quit() method to Service interface

https://play.golang.org/p/gN21yO9IRs3

```
func waitWithCancel(f func() *clist.CElement, ctx context.Context) *clist.CElement {
	el := make(chan *clist.CElement, 1)
	select {
	case el <- f():
```
will just run f() blockingly, so this doesn't change much in terms of behavior.

See https://github.com/tendermint/tmlibs/issues/45

```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x882cec]

goroutine 328 [running]:
github.com/tendermint/tendermint/p2p.(*Switch).DialPeerWithAddress(0xc42000a500, 0xc4202088d0, 0xc420403500, 0x0, 0x0, 0x0)
        /home/vagrant/go/src/github.com/tendermint/tendermint/p2p/switch.go:324 +0x2fc
github.com/tendermint/tendermint/p2p.(*PEXReactor).ensurePeers.func1(0xc4201663f0, 0xc4202088d0)
        /home/vagrant/go/src/github.com/tendermint/tendermint/p2p/pex_reactor.go:280 +0x3e
created by github.com/tendermint/tendermint/p2p.(*PEXReactor).ensurePeers
        /home/vagrant/go/src/github.com/tendermint/tendermint/p2p/pex_reactor.go:284 +0x5d4
```