Parameterize the deployment of server web site
Servers pages should be provided at standard locations, like
Currently, eglide and dwellers store at the default nginx
directory their respective homepages.
As a first step in this direction, a node.get_wwroot helps
to determine from a server hostname the directory to use.
Another issue is nginx is installed under www-data on Debian,
while on FreeBSD it's installed as www. There is also a custom
group declared in webserver-legacy account unit.
Test Plan: Ensure it's no-op on Eglide
Reviewed By: dereckson
Differential Revision: https://devcentral.nasqueron.org/D1253