[WFLY-561] Infinispan subsystem -- statistics becomes statistics-enabled

Infinispan part of the to-be-closed #5609.

This is a simple rename of an attribute added in WF 8 and, if Paul approves, is important to get into CR1, or at least Final. The other WFLY-561 changes are less critical as they involve correcting flaws in previous Final releases. This one prevents a new flaw.