adds ppa:nginx to apt repositories when
nginx_use_ppa is set to yes (default no)
nginx_ppa_version can be either "stable" or "development"
this will reinstall nginx if ppa was just added to ensure that the ppa
version will be installed
NOTE: current nginx config validation process breaks SELinux context
for pid file, as described in #41
Restart of nginx is not needed for configuration changes and is
replaced with reload, which will validate config before applying it,
leaving running nginx process untouched in case of any validation
errors.
Restart handler left in support.
Re-ordering the tasks in this way (having the vhosts deployed first)
allows the 'validate' param to collectively check the deployed Nginx config.
Deploying vhosts after makes it hard to check their validity, as Nginx's
config checking will operate on a "master" configuration that includes
others (checking those included, also) but would error out when checking
these individual configs if they do not contain a fully working Nginx
config (which they often don't, due to their nature).
