Allow docroot with mod_vhost_alias virtual_docroot

[yakatz]

DocumentRoot is used for other directives when a Virtual Document Root is not found.
For backwards compatibility, docroot is still ignored unless you set the virtual_use_default_docroot to true.

For example, to show a custom 404 message, you might use mod_rewrite, but that needs a DocumentRoot to be set:

# ************************************
# Vhost template in module puppetlabs-apache
# Managed by Puppet
# ************************************
#
<VirtualHost *:80>
  ServerName projects.example.com

  ## Vhost docroot
  VirtualDocumentRoot "/var/www/projects/_webroots/%0"
  DocumentRoot "/var/www/projects/_webroots"

  ## Directories, there should at least be a declaration for /fs/www/projects/_webroots

  <Directory "/fs/www/projects">
    Options FollowSymLinks MultiViews Indexes
    AllowOverride None
    Require all granted
  </Directory>

  ## Logging
  ErrorLog "/var/log/httpd/projects.cs.umd.edu_error.log"

  ## Rewrite rules
  RewriteEngine On

  #Show errors for missing sites
  RewriteCond %{HTTP_HOST} "^([^:/]*)(:.+)?" [NC]
  RewriteCond '/var/www/projects/_webroots/%1' !-d
  RewriteRule (.*) /default-site/index.php [L]


  UseCanonicalName Off
</VirtualHost>

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[puppet-community-rangefinder]

apache::vhost is a type

that may have no external impact to Forge modules.

This module is declared in 173 of 578 indexed public Puppetfiles.

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[yakatz]

Fixed.

[david22swan]

LGTM

[david22swan]

@yakatz Thanks for putting in the work.
This looks good to me so I'm gonna go ahead and merge.
Looking forward to more from you in the future