Support properties placeholders on infinispan configuration files

Currently all values configured in infinispan.xml need to be hardcoded in the file as System property placeholders are not supported.
There are many cases when it's not ideal to have the values there for example when configuring a jdbc cache store, the db, user, pass, etc... need to be hardcoded for the configuration to work.
Ideally infinispan would resolve placeholders such as ${jdbc.user} to a predefined system property or a property file, with that name in the same way other frameworks like spring, ant, maven, etc... do.