Bug 12312 - correctly upgrade under Apache 2.2

As the way we need to reference Apache instance names has now changed
between 2.2 and 2.4, we need to try it out both ways to make sure we get
it right.

This also allows koha-create/koha-disable to try the .conf version of
the name if the first one doesn't work.

To test:
* Create an instance on an Apache 2.2 system with koha < 3.16
* Upgrade to 3.16 with this patch, saying 'yes' to the renaming question
** Make sure you don't see the warning: Warning: problem enabling $site
   in Apache
* Do a 'service apache2 restart'
* Make sure you can still access the instance
* Make sure that /etc/apache2/sites-enabled/instance.conf exists as a link
  to /etc/apache2/sites-available/instance.conf
* Check that koha-create and koha-remove behave like you'd expect.

Note:
* If you need to make debconf forget that it asked you the question
  about renaming so that it'll do it again, then run:
  echo "unregister koha-common/rename-apache-vhost-files" | sudo debconf-communicate koha-common
* 'debconf-show koha-common' will show you the current debconf
  configuration.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>