core: Cache JNDI lookups and InitialContext creation

This patch caches the lookup for resources and local EJBs in the server.
The goal is to improve performance.

Change-Id: I45ae8d0a90a03c498e19e5429d196924671c073b
Signed-off-by: lzelkha@redhat.com <liran.zelkha@gmail.com>