insert 'realm' in role::cache::configuration::active_nodes

With the recent rewrites, the $actives_nodes need to vary by realm just
like $backends.

I have changed the squid cache manager configuration as well as the
torrus templates.

Change-Id: Ia6e39dc0b2ccff43f2c7501a1239055c7d9d56b9
Merge "insert 'realm' in role::cache::configuration::active_nodes" into production