constantly relookup ip for etcd host

to ensure that you don't wind up in a race
condition that I have seen where the lookup
call returns the private address b/c the
public one is not assigned yet.

this will continuously re-lookup the address
until the specified command works.
Use single quotes to make escaping simpler
Export project_tag so that it can be looked up in subshells
Also set ip variable outside that loop
Merge pull request #185 from sorenh/relookup_etcd_ip

constantly relookup ip for etcd host