Update /etc/hosts when linked container is restarted

Carry of #7092

closes #7092
fixes #6350

/cc @vieux
Agree with Sonat, and would ask you to please go a step further and simply remove any reference of "parent" or "child" in the docs (I realize it's in the code, c'est la vie). In #7250 we determined it simply is not the right metaphor.

If you need to get the PR in asap, LMK and I'll make a reminder to go back and edit it myself.