setup nginx for load balancing, setting HOME variable in unicorn_init, and fix for missing nginx log directory when web is a non-release role

- (temporary?) fix to problem in unicorn_init script whereby HOME variable is not set (possible alternative to https://github.com/bruno-/capistrano-unicorn-nginx/pull/11)
- create log directory for nginx if web is a non-release role
- connect over TCP/IP if there are multiple app roles and setup nginx for load balancing
Did you try overwriting unicorn initializer file?
The `setup_initializer` task can't simply be overwritten, I just tried doing this manually and I get the error:

    System start/stop links for /etc/init.d/unicorn_blog_production already exist.

I think the overwrite feature is nice, but it's definitely not the core for the nginx load balancing plugin update.

@rhomeister may I suggest we completely remove the 'config overwrite' feature from this pull request and open a new one for it?
A quick idea for the new pull request: why even explicitly check if we want to overwrite config files. Why not overwrite them each time `setup` task is invoked.