PROTON-603: testCreditReclaim fails on windows
The issue is that during 'while client2.work(0): self.pump()' 
on windows the credit rebalancing is already happening. 
Testing that it hasn't yet happened causes the failure. 
The only safe thing to do is to keep calling pump and 
verify that the expected credits are achieved eventually.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1602016 13f79535-47bb-0310-9956-ffa450edef68