Sometimes it's necessary optimization in nginx+apache2 environment

Added example shows 503 code instead of "It works!" page.

By reassigning options with `blockreplace` at `/etc/apache2/conf-available/security.conf`, which is linked as conf-enabled by default on Debian packages

Add `onlyif` check to execute `a2dissite` only when needed.

DocumentRoot is useless for a plain redirect or proxy vhost, no need to
force creating the directory.

Signed-off-by: Julien Cristau <julien.cristau@logilab.fr>

* Add apache version (2.2, 2.4) detection based on osfinger (defaults to 2.4).
* Version can be overridden in pillar (for Apache 2.4 on RHEL 6 for example)

- Added more modules and configuration options
 - Renamed sls files to reflect what they do.
 - added mpm options for Debian

Fix check for SSLCertificateFile, SSLCertificateKeyFile variables in vhosts/standard.tmpl, now using dict.get()