Fix org.jboss.test.ws.jaxws.as3581.AS3581TestCase

The org.jboss.test.ws.jaxws.as3581.AS3581TestCase shows intermittent failures on Hudson. The reason is likely that the test first call a @Oneway method to have a server class static member initialized with a given value, then it invokes a req-res method on another endpoint to get the current value of the previously initialized static member. The problem is likely that the member initialization might have not been completed by the time the req-res invocation is performed, given the first invocation is basically fire & forget @Oneway.