Split advertised address from listen address

There are currently problems with "swarm init" and "swarm join" when an
explicit --listen-addr flag is not provided. swarmkit defaults to
finding the IP address associated with the default route, and in cloud
setups this is often the wrong choice.

Introduce a notion of "advertised address", with the client flag
--advertise-addr, and the daemon flag --swarm-default-advertise-addr to
provide a default. The default listening address is now 0.0.0.0, but a
valid advertised address must be detected or specified.

If no explicit advertised address is specified, error out if there is
more than one usable candidate IP address on the system. This requires a
user to explicitly choose instead of letting swarmkit make the wrong
choice. For the purposes of this autodetection, we ignore certain
interfaces that are unlikely to be relevant (currently docker*).

The user is also required to choose a listen address on swarm init if
they specify an explicit advertise address that is a hostname or an IP
address that's not local to the system. This is a requirement for
overlay networking.

Also support specifying interface names to --listen-addr,
--advertise-addr, and the daemon flag --swarm-default-advertise-addr.
This will fail if the interface has multiple IP addresses (unless it has
a single IPv4 address and a single IPv6 address - then we resolve the
tie in favor of IPv4).

This change also exposes the node's externally-reachable address in
docker info, as requested by #24017.

Make corresponding API and CLI docs changes.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

docs/reference/commandline/dockerd.md

@@ -69,6 +69,7 @@ Options:
       -s, --storage-driver                   Storage driver to use
       --selinux-enabled                      Enable selinux support
       --storage-opt=[]                       Storage driver options
+      --swarm-default-advertise-addr         Set default address or interface for swarm advertised address
       --tls                                  Use TLS; implied by --tlsverify
       --tlscacert=~/.docker/ca.pem           Trust certs signed only by this CA
       --tlscert=~/.docker/cert.pem           Path to TLS certificate file
@@ -1042,6 +1043,7 @@ This is a full example of the allowed configuration options on Linux:
 	"tlscacert": "",
 	"tlscert": "",
 	"tlskey": "",
+	"swarm-default-advertise-addr": "",
 	"api-cors-header": "",
 	"selinux-enabled": false,
 	"userns-remap": "",
@@ -1112,6 +1114,7 @@ This is a full example of the allowed configuration options on Windows:
     "tlscacert": "",
     "tlscert": "",
     "tlskey": "",
+    "swarm-default-advertise-addr": "",
     "group": "",
     "default-ulimits": {},
     "bridge": "",