poll pool stats in loop instead of Thread.sleep in AbstractDatasourceCapacityPoliciesTestCase

There is Thread.sleep in AbstractDatasourceCapacityPoliciesTestCase.java#L130 and ResourceAdapterCapacityPoliciesTestCase.java#L148 which is used to wait until pool is filled with expected number of connections. But it is generally better to loop around for a while until things are in the right state, and then fail if that state does not happen within a (adjustable) timeout