Remove redundant shell function

This was used before http_call was made, but that function effectively
inlines it.
Merge pull request #210 from squaremo/remove_redundant_shellfunc

Remove redundant shell function
Set 'Unsafe' flag to allow dns.Server to handle responses
Rename 'server' to 'listener' to better match how it is used
fix typo
Merge pull request #215 from sw1nn/patch-1

fix typo
Merge branch 'master' of github.com:bboreham/weave into pr213
Add more links to Boot2Docker info
Populate DNS when starting the weaveDNS container
Only get the DNS container IP once

`populate_dns` previously used http_call, which looks up the IP for a
container each time. I've factored the HTTP bit after the IP look-up
in http_call out, so it can be used directly. This involved switching
arguments around to make the tail call easier.