Make weave IP preferred in /etc/hosts lookup, for 'attach'-ed addresses

[bboreham]

Remainder of #68, following merge of #1079.

A container started outside of weave and then attach-ed will have two IP addresses: one assigned by Docker and one assigned through weave. So hostname -I will return something like:

root@9b903541c5a7:/# hostname -I
172.17.0.72 10.0.0.61 

however, hostname -i returns the Docker-assigned IP:

root@9b903541c5a7:/# hostname -i
172.17.0.72

See conversation in #68 for justification.

[rade]

This might get fixed by #1477.

[inercia]

With #1477 :

root@094ab31b017d:/# hostname -I
172.17.0.121 10.32.0.2 
root@094ab31b017d:/# hostname -i
10.32.0.2

[rade]

I don't see how #1477, in its current form, can fix this, since there weave attach only rewrites /etc/hosts when called with a --rewrite-hosts option. And there is no simple fix for that either since a) we'd somehow need to get hold of the extra hosts from the --add-host options that were supplied on startup, and b) get hold of all weave IPs for a container so we don't populate /etc/hosts with partial information. Both of these are do-able but fiddly, so best left to a separate PR.

@inercia is my understanding correct?

[rade]

#1477 does however, take care of rewriting /etc/hosts on weave run. Which is nice.

[yaronr]

+1