calamari-server.postinst: 'a2enmod version' so IfVersion works on precise

Fixes: #9163
Signed-off-by: Dan Mick <dan.mick@inktank.com>
Merge pull request #182 from ceph/wip-9163

calamari-server.postinst: 'a2enmod version' so IfVersion works on precis...