Failing to boot the ORM integration no longer throws an exception

Due to the work I've done to make the boot code simpler and more similar when booting in synchronous and asynchronous mode, we no longer throw an exception in the session observer when Hibernate Search fails to boot: the exception is logged and will be propagated on the first access to Hibernate Search.

It's the best we can do when booting in asynchronous mode (waiting for CDI to be ready), but when booting in synchronous mode we really should throw the exception ASAP.