[FAB-9159] fix data race in kafka logger test
[FAB-9159] fix data race in kafka logger test

bytes.Buffer does not support concurrent access but gbytes.Buffer does.

Change-Id: I1f23ad3addba4c4517666861b87cdcfd38757238
Signed-off-by: Matthew Sykes <89c6e4c9c1046731a9c37abefc223a83de36a5d9@us.ibm.com>

hyperledger/fabric,manish-sethi/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,binhn/fabric,manish-sethi/fabric-sidedb,muralisrini/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,stemlending/fabric,manish-sethi/fabric-sidedb,xixuejia/fabric,jimthematrix/fabric,muralisrini/fabric,xixuejia/fabric,manish-sethi/fabric-sidedb,stemlending/fabric,binhn/fabric,muralisrini/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,jimthematrix/fabric,stemlending/fabric,xixuejia/fabric,binhn/fabric