make '/var/www' be mounted as 'www-data'

This avoids permission problems while writing files in there. Got some of those errors while implementing hhvm as an additional FastCGI upstream.
Merge pull request #9 from hexa2k9/hotfix/mount-options

make '/var/www' be mounted as 'www-data'
Merge branch 'refs/heads/master' into feature/hhvm
run hhvm as www-data