Configure ::mediawiki and ::mysql with hiera

Use hiera to provide parameters for the mediawiki and mysql classes.
This allows us to reduce role::mediawiki to a collection of classes to
apply without specifying a lot of configuration data in the role itself.

Merge role::generic and role::mysql into role::mediawiki since they were
included there and are not specifying configuration data any longer.

Additionally convert all the sub-classes in ::mediawiki to hiera as
well.

Several roles were touched because they referenced variables that
were previously set in role::mediawiki.

Change-Id: I74b304107ca9d97d455941bb6f07759d45e3b5a1
Merge "Configure ::mediawiki and ::mysql with hiera"