Bug came up in a test where we are restarting and doing an exec checking
a network interface right away. weavewait is only added if the container
has a WEAVE_CIDR var set, the same as at container creation.
In the proxy, I swapped the 'flag' library for
'code.google.com/p/getopt', which uses double-dash flags.
proxy lets 'weave attach' do dns registration on container start
proxy needs to set DNSSearch if not specified
Paul Bellamy