beta: fix mediawiki dependency

(File[/usr/local/apache] => Package[wikimedia-task-appserver] =>
Class[Mediawiki::Packages] => Class[Mediawiki::Sync] =>
File[/usr/local/apache])

We can not require the package and require a file that should be done
before the package. Instead, create the file directly in the package
class, that make sense since both the file and package are used to
create /usr/local/apache/.

Change-Id: I88bad8d686a1d8ebc8a0e3683c3d34e0ae335a75