[HORNETQ-1381][2.4.x] creates HornetQ threads in a privileged block

JIRA: https://issues.jboss.org/browse/HORNETQ-1381
Merge pull request #1753 from jmesnil/HORNETQ-1381_thread_factory_security_manager_2.4.x

[HORNETQ-1381][2.4.x] creates HornetQ threads under a security manager