zuul: introduced config hash in role::zuul::configuration

I would like to split the role class between server/merger instead of
between realms.

The roles used in production and labs are very similiar. Based on the
existing role::cache::configuration, this introduce configuration hash
with $::realm as key. Let us easily change the configuration and we will
later on be able to share the same role class on both labs and
production.

Change-Id: I3699567354b4fbb540c1d4e4aaafbd41ed31db6f
Merge "zuul: introduced config hash in role::zuul::configuration" into production