using assertTrueEventually to wait for the nearCash to be cleared

this test had a high freq of failing at this assert,  looking at the history of build/Test is shows nearCash size is approaching 0
test fails on latch wait (not enough time to eviect enterys)  or map.size < expected so the inner Thread did not have enough time to get the enterys and save them from evection
Merge pull request #1530 from Danny-Hazelcast/nearCashTestFix

using assertTrueEventually to wait for the nearCash to be cleared