HornetQ security manager doPrivileged() block

move all HornetQ user and roles validation into a single
AccessController.doPrivileged() block.
validateUserAndRole() is called from a thread in HornetQ own's thread
pool. Calling it inside  a doPrivileged() block ensures that the code
will not raise an AccessControlException when WildFlySecurityManager
checks the permissions.
Group all the doPrivileged blocks into a single one.