invenio-setup-prerequisites: fix for Ubuntu 14.04 LTS

* Switches from openoffice.org to libreoffice.

* Disables 000-default as well as default-ssl using wildcard.

* Renames vhost configuration to .conf otherwise a2ensite doesn't see
  them.

* Enables mod_version if possible.

* Supports being run from a virtualenv.

Signed-off-by: Yoan Blanc <yoan.blanc@cern.ch>