php: apc: parametrising apc.ttl and apc.user_ttl.
Ideally, these are 0, but with mod_vhost_alias, when there could be many
docroots, it's safer to have a non-infinite TTL.
The parameter can be controlled via hieradata, utilising automatic
parameter lookup:
https://docs.puppetlabs.com/hiera/1/puppet.html#automatic-parameter-lookup