Passes up an error if we fail to get an address

[slackpad]

This fixes hashicorp/consul#3312.

[junjies]

hello, I get error like this, could you anyone help ?

sudo /usr/local/bin/consul agent -config-dir /etc/consul.d

==> WARNING: Expect Mode enabled, expecting 3 servers
==> Starting Consul agent...
==> Error starting agent: Failed to start Consul server: Failed to start LAN Serf: Failed to create memberlist: Could not set up network transport: ran out of tries to obtain an address

Thanks.

[slackpad]

HI @junjies this change will propagate the error that's causing the issue up so it's visible. This should ship tomorrow in Consul 0.9.1. It's usually that Consul is unable to bind to the given port or interface.