Disable pooling of stateless EJBs by default

A certain use case has shown that it's perhaps better to disable pooling of EJB stateless bean, by default. In AS7 we have always allowed disabling the pooling but we hadn't made it the default since we thought it might affect applications which have SLSBs with heavy @PostConstruct.

A recent discussion has suggested that we disable the pooling by default and individual applications can enable it and set the relevant pool size themselves. The reasoning has been that, the default pool size that we ship with, anyway will have to be tweaked by the users since we can't really guess what an ideal pool size is.