WFLY-1383 Disable pooling of stateless EJBs, by default

The commit here disables pooling of stateless EJBs by default. This relates to https://issues.jboss.org/browse/WFLY-1383. 

Although this disables pooling by default for SLSBs, it intentionally leaves around the SLSB pool configuration(s) which have been shipped in previous releases. This allows (existing) user applications to still rely on them (for example through the use of @Pool(name="slsb-strict-max-pool"). It will also serve as an example pool configuration.

Individual applications which require pooling of stateless EJBs can configure it either individually at the bean level or by re-enabling this at the subsytem level.