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()

If the DocumentRoot value wasn't set, applying the state would cause the
following error:

          ID: site.example.com-documentroot
    Function: file.directory
        Name: None
      Result: False
     Comment: Specified file None is not an absolute path
     Started: 15:07:05.596723
    Duration: 4.929 ms
     Changes:

This fixes the problem by not trying to check for the DocumentRoot directory is
the value is missing.

Make sure that you can makedirs incase parent folders are not created

Create the vhost DocumentRoot directory if it does not exist

Add optional templating for the register site aspect of a pillar.

User can specify keys to be included as defaults, otherwise it is
treated as a normal managed file.

This is more reliable than version numbers which might change with point
releases (in particular for Debian Jessie) and is more likely to not
conflict between multiple OS.