[HORNETQ-1357] Load class from priviledged access block

If the security manager is set, resolve the class inside a priviledged
access block

JIRA: https://issues.jboss.org/browse/HORNETQ-1357
[HORNETQ-1358] Create journal files from privileged access block

If the security manager is set, create the journal files from a
privileged access block to have the correct FilePermission

JIRA: https://issues.jboss.org/browse/HORNETQ-1358